Thermal hemostasis and/or coagulation of tissue

ABSTRACT

Energy delivery systems and methods are provided for use in biological tissue. The energy delivery system includes an energy source and an electrode array. The electrode array includes bipolar electrodes positioned so a first spacing between a pair of adjacent electrodes is different relative to a second spacing between at least one other pair of adjacent electrodes. The electrode array and the energy source are coupled and configured to generate uniform energy density in target tissue according to impedance of the target tissue.

RELATED APPLICATIONS

This application claims the benefit of U.S. Patent Application No.60/644,721, filed Jan. 18, 2005.

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 11/256,500, filed Oct. 20, 2005, which is acontinuation-in-part application of U.S. patent application Ser. No.10/890,055, filed Jul. 12, 2004, which is a continuation in partapplication of U.S. patent application Ser. No. 10/800,451, filed Mar.15, 2004, which is a continuation-in-part application of InternationalApplication Number PCT/US03/21766, filed Jul. 11, 2003, and acontinuation-in-part application of U.S. patent application Ser. No.10/413,112, filed Apr. 14, 2003, which application claims the benefit ofU.S. Patent Application No. 60/405,051, filed Aug. 21, 2002.

TECHNICAL FIELD

This invention relates generally to tissue coagulation and the resectionof tissue, and more particularly to the creation of planar tissuecoagulations using radio frequency (“RF”) energy.

BACKGROUND

Standard surgical procedures, such as resection, for treating variousmaladies of different organs like the liver, kidney, and spleen thatinclude such things such as tumors, injuries from trauma, and such haveseveral key shortcomings. These shortcomings affect efficacy, morbidityand mortality to name a few. A fundamental issue for example is theinability to adequately control blood loss during the tissuetransection.

In an attempt to help overcome this limitation various mono-polar andbi-polar RF devices have been created. These devices act as conduits todeliver energy from an RF generator. These devices include electrocautrypencils and probes of various types and configurations from a number ofdifferent manufactures such as Bovie, ValleyLab, and TissueLink. Thealgorithms currently used with these devices in surgical treatmentstypically provide a constant amount of delivered energy in which thepower level and duration are directly controlled by the user. Thisapproach suffers from fundamental flaws that limit their usefulness in atypical clinical setting.

The flaws associated with delivering a constant amount of energy totarget tissue include an inability to automatically adjust to thecorrect level of energy delivery by properly responding to the conditionof the tissue to be transected. After the initial application of energyto the target tissue the properties of the tissue begin to change. Withthese changes the application of energy should also change in order tomaintain an optimum energy application. The typical methods ofdelivering hemostatic energy to the target tissue are ill-suited becausethey rely on the user to adjust the energy delivery with little or noinformation or guidance as to the changing state of the target tissue.As a result the ultimate amount or duration of delivered energy maybeinsufficient for creating hemostasis.

Furthermore, the typical energy delivery systems rely on the user to setthe initial level of energy delivery with little or no relevantinformation of the condition of the target tissue being treated.Therefore, when using the typical energy delivery systems, the initialapplication of energy can be significantly lower or higher than what isneeded. When an inadequate amount of energy is applied to the targettissue, a haemostatic tissue effect is not achieved. Likewise, if theduration of the energy application is too short, proper hemostasis willnot be achieved. When an excessively high amount of energy is applied tothe target tissue the result can be carbonization of the target tissue.This carbonization can prevent the continued flow of delivered energy tothe tissue; it also often creates an overly superficial depth of treatedtissue resulting in poor hemostasis.

INCORPORATION BY REFERENCE

Each publication, patent and/or patent application mentioned in thisspecification is herein incorporated by reference in its entirety to thesame extent as if each individual publication, patent and/or patentapplication was specifically and individually indicated to beincorporated by reference.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a tissue coagulation system, under an embodiment.

FIG. 2 and FIG. 3 are schematics of the energy director guide, includingvarious views, under an embodiment.

FIG. 4A shows a resistive network model for an energy directorconfiguration including six (6) energy directors, under the embodimentof FIGS. 2 and 3.

FIG. 4B shows a table including power dissipation values correspondingto an energy director configuration providing balanced energy, under theembodiment of FIG. 4A.

FIG. 4C is a table including power dissipation and spacing informationcorresponding to an energy director configuration providing balancedenergy, under the embodiment of FIG. 4A.

FIG. 5A shows a resistive network model for an energy directorconfiguration including eight (8) energy directors, under an alternativeembodiment.

FIG. 5B shows a table including power dissipation values correspondingto an energy director configuration providing balanced energy, under theembodiment of FIG. 5A.

FIG. 5C is a table including power dissipation and spacing informationcorresponding to an energy director configuration providing balancedenergy, under the embodiment of FIG. 5A.

FIG. 6A shows a resistive network model for an energy directorconfiguration including six (6) energy directors (five zones), under analternative embodiment.

FIG. 6B shows a table including power dissipation informationcorresponding to an energy director configuration providing balancedenergy, under the embodiment of FIG. 6A.

FIG. 6C is a table including current and spacing informationcorresponding to an energy director configuration providing balancedenergy, under the embodiment of FIG. 6A.

FIG. 7 is an energy director guide and energy directors, under analternative embodiment.

FIG. 8 is a side view of an energy director guide using direct coupling,under an embodiment.

FIG. 9 is a schematic of a circuit board for use in an energy directorguide, under the embodiment of FIG. 2.

FIG. 10 is a side view of an energy director guide using indirectcoupling, under an embodiment.

FIG. 11 shows an energy director guide that provides for independentcontrol of the insertion depth of each energy director, under anembodiment.

FIG. 12 and FIG. 13 show operation of the tissue coagulation system togenerate an avascular volume of tissue, under the embodiment of FIG. 2.

FIG. 14 is a flow diagram for the operation of the tissue coagulationsystem, under an embodiment.

FIG. 15 is a flow diagram for controlling tissue coagulation inaccordance with temperature parameters, under an embodiment.

FIG. 16 is a flow diagram for controlling tissue coagulation inaccordance with impedance and time parameters, under an embodiment.

FIG. 17 is a flow diagram for controlling tissue coagulation inaccordance with impedance parameters, under an embodiment.

FIG. 18 is a plot of impedance and power versus time for use incontrolling tissue coagulation, under an embodiment.

FIG. 19 is a plot of time verses impedance depicting an effective tissuecoagulation cycle, under an embodiment.

FIG. 20 is a plot of time verses impedance depicting an undesirably lowlevel of delivered power, under an embodiment.

FIG. 21 is a plot of time verses impedance depicting an undesirably highlevel of delivered power, under an embodiment.

FIG. 22 is a flow chart for effective tissue coagulation, under theembodiment of FIG. 19.

FIG. 23 shows a flexible or semi-flexible guide having flexibility intwo planes, under an alternative embodiment.

FIG. 24 shows a flexible or semi-flexible guide having flexibility inone plane, under another alternative embodiment.

FIG. 25 is an energy director array including a joining member thatprovides for simultaneous insertion or retraction of energy directorsinto target tissue, under an embodiment.

FIG. 26 is an energy director array including a joining member connectedto energy directors, under an alternative embodiment.

FIG. 27 shows energy directors supporting delivery of various agentsinto the target tissue, under an embodiment.

FIG. 28 shows energy directors that capacitively couple to targettissue, under an embodiment.

In the drawings, the same reference numbers identify identical orsubstantially similar elements or acts. To easily identify thediscussion of any particular element or act, the most significant digitor digits in a reference number refer to the Figure number in which thatelement is first introduced (e.g., element 102 is first introduced anddiscussed with respect to FIG. 1).

DETAILED DESCRIPTION

A tissue coagulation system including numerous components and methods isdescribed in detail herein. The tissue coagulation system generates anavascular volume of coagulated tissue that aids in the bloodless ornear-bloodless resection of various biological tissues from a variety oforgans including, for example, the liver, spleen, kidney, and variousother organs of the body. The terms coagulation, thermal coagulation,ablation, coagulative ablation, and thermal ablation all have the samemeaning for purposes of the description below and can be usedinterchangeably.

In the following description, numerous specific details are introducedto provide a thorough understanding of, and enabling description for,embodiments of the tissue coagulation system. One skilled in therelevant art, however, will recognize that the tissue coagulation systemcan be practiced without one or more of the specific details, or withother components, systems, etc. In other instances, well-knownstructures or operations are not shown, or are not described in detail,to avoid obscuring aspects of the tissue coagulation system.

FIG. 1 is a tissue coagulation system 100, under an embodiment. Thetissue coagulation system 100 includes an energy director guide 102, orguide, and two or more pair 104 of bipolar energy directors, alsoreferred to herein as electrodes. The tissue coagulation system 100 isused for the thermal coagulation necrosis of soft tissues as an aidduring tissue resection. Alternative embodiments of the tissuecoagulation system 100 can include monopolar energy directors andvarious combinations of bipolar and monopolar energy directors. Theenergy directors 104 are configured for insertion into a volume ofbiological tissue 199. The energy director guide 102 configures theenergy directors to provide approximately uniform power or energydistribution through a tissue volume, referred to as the target tissueor target tissue volume. The target tissue volume includes the volumewithin an approximately one (1) centimeter (“cm”) radius around eachenergy director 104 extending over the conducting length of the energydirector 104, but is not so limited. The target tissue volume forms atleast one plane of coagulated tissue.

The energy director guide 102 and the energy directors 104 are coupledamong at least one generator 110, or power source, but are not solimited. The energy directors 104 of an embodiment couple to thegenerator 110 via the energy director guide 102. Alternatively, theenergy directors 104 can couple directly to the generator 110 via awire, cable, or other conduit.

Using the bipolar configuration of the energy directors 104, oneelectrode of an electrode pair serves as a source and the otherelectrode of the pair serves as a sink for the power received from thegenerator 110. Therefore, one electrode is disposed at the oppositevoltage (pole) to the other so that power from the generator is drawndirectly from one electrode to the other. The bipolar electrodearrangement insures more localized and smaller heat coagulation volumes,but the embodiment is not so limited.

The alternating polarity series of energy directors includes variousseries combinations of alternating polarities. For example, in anembodiment using six (6) energy directors, the alternating polarity is:positive polarity (+), negative polarity (−), +, −, +, −. An alternativepolarity series is: +, +, −, −, +, +. Another alternative polarityseries is: −, −, +, +, −, −. Yet another alternative polarity series is:+, +, +, −, −, −. Still other alternative polarity series can include:+, +, −, +, −, −. These examples are exemplary only, and the tissuecoagulation system 100 described herein is not limited to six (6)electrodes or to these alternating polarities.

The energy directors 104, while configured appropriately for insertioninto particular tissue types, have a shape and a pattern that supportscoupling to the target tissue and allows the energy directors 104 todeliver sufficient energy to cause the tissue to become hemostatic, suchas by coagulation of the tissue, thereby facilitating resection of aselected tissue volume. The energy directors 104 of an embodimentinclude rigid shafts that are of sufficient stiffness to be easily urgedinto the target tissue 199 and coupled to the tissue 199 while retainingtheir shape.

The energy directors 104 terminate in non- or minimally-traumatictissue-penetrating tips of various configurations known in the art asappropriate to the tissue type of the target tissue 199. The energydirector tip configurations of an embodiment include fully rounded tips,flat tips, blunt tips, and rounded tips, but are not so limited. Theseconfigurations facilitate insertion of the energy directors intodifferent types of target tissue while protecting the user from sharppoints that, during normal handling, pose a puncture hazard to the user.This is particularly important since the energy directors could becontaminated with potentially deadly material including viruses such asHepatitis-C and Human Immunodeficiency Virus (“HIV”) that could betransmitted to the user through a puncture wound.

The energy directors of an embodiment can have many different sizesdepending upon the energy delivery parameters (current, impedance, etc.)of the corresponding system. For example, energy director diameters areapproximately in the range of 0.015 inches to 0.125 inches, but are notso limited. Energy director lengths are approximately in the range of 4cm to 10 cm, but are not so limited. Energy directors include materialsselected from among conductive or plated plastics, super alloysincluding shape memory alloys, and stainless steel, to name a few.

Further, an array of energy directors can include energy directors ofdifferent sizes and lengths. For example, an energy director array of anembodiment includes six (6) energy directors in a linear array, wherethe energy director on each end of the array is a 16-gage electrodewhile the four (4) energy directors that form the center of the arrayare 15-gage electrodes. The use of energy directors having differentdiameters allows for balancing of energy/energy density in the targettissue by, for example, decreasing the total energy dissipation in thetarget tissue at the ends of the array (smaller energy directors) andthereby limiting/controlling the effect (necrosis) on the tissue beyondthe ends of the energy director array. Therefore, the use of energydirectors having different diameters provides an additional means ofcontrol over energy balancing in the target tissue in addition to thespacing between the energy directors.

The energy directors 104 of various alternative embodiments can includematerials that support bending and/or shaping of the energy directors104. Further, the energy directors 104 of alternative embodiments caninclude non-conducting materials, coatings, and/or coverings in varioussegments and/or proportions along the shaft of the energy director 104as appropriate to the energy delivery requirements of the correspondingprocedure and/or the type of target tissue.

The generator 110 of an embodiment delivers pre-specified amounts ofenergy at selectable frequencies in order to coagulate and/or cuttissue, but is not so limited. The generator 110 of an embodiment is anRF generator that supports output power in the range of approximatelyzero to 200 Watts, output current in the range of approximately 0.1 ampsto four (4) amps, and output impedances generally in the range ofapproximately two (2) to 150 Ohms, across a frequency range ofapproximately one (1) kHz to 1 MHz, but is not so limited.

It is understood that variations in the choice of electrical outputparameters from the generator to monitor or control the tissuecoagulation process may vary widely depending on tissue type, operatorexperience, technique, and/or preference. For example, in one embodimenta common voltage is applied to all the energy directors of an arraysimultaneously. As an alternative embodiment, the operator may choose tocontrol the current to the individual energy directors of the array orthe total current of the array as a whole.

Further, voltage variations on each energy director can be applied toachieve constant current output from each energy director.Alternatively, constant power output from each energy director may besought in some procedures. Additionally, voltage variations or phasedifferences between energy directors can be implemented to achievepre-specified temperature distributions in the tissue as monitored bytemperature sensors in the tissue or by visualization of temperaturedistribution using techniques known in the art. Accordingly, the choiceof electrical output type, sequence, and levels and the distribution tothe energy directors of the array should be considered to have widevariations within the scope of this invention.

Various geometric factors relating to the target tissue also affect theheating of tissue during coagulation. These include the tissue edges aswell as the coagulation surface volume. As the amount of ablativesurface area increases, the heat loss also increases. Coagulation edges,sides, and ends all can have an effect on the heat loss duringcoagulation.

The coagulation system of an embodiment ablates the target tissue byheating the tissue uniformly between the energy directors. In order toaccomplish the uniform heating, the current density in the tissueimmediately surrounding the energy conduit should not be significantlygreater than the current density in the tissue between the energyconduits. As an example, consider the case where the size of theelectrode is relatively small so that the tissue/energy conduit contactarea is small. This results in a high currently density around theenergy conduit leading to dominant heating in the immediate vicinity ofthe electrodes, increasing the probability of unwanted tissue charringand ultimately limiting the amount of energy that can be delivered tothe tissue. Methods provided herein to address this include using alarger tissue/energy conduit contact area, cooling the electrode, andintroducing a more conductive material around the electrode area, forexample hypertonic saline.

The tissue coagulation system 100 can include any number of additionalcomponents like, for example, a controller 120 to semi-automatically orautomatically control delivery of energy from the generator. Thecontroller can, for example, increase the power output to theelectrodes, control temperature when the energy directors includetemperature sensors or when receiving temperature information fromremote sensors, and/or monitor or control impedance, power, current,voltage, and/or other output parameters. The functions of the controller120 can be integrated with those of the generator 110, can be integratedwith other components of the tissue coagulation system 100, or can be inthe form of stand-alone units coupled among components of the tissuecoagulation system 100, but are not so limited.

Moreover, the tissue coagulation system 100 can include a display 130that provides a display of heating parameters such as temperature forone or more of the energy directors, impedance, power, current, timinginformation, and/or voltage of the generator output. The functions ofthe display 130 can be integrated with those of the generator 110, canbe integrated with other components of the tissue coagulation system100, or can be in the form of stand-alone units coupled among componentsof the tissue coagulation system 100, but are not so limited.

Various alternative embodiments of the tissue coagulation system 200 canalso include a biocompatible thermal shield 140. The thermal shield 140serves to protect the organs and tissue that surround the targetbiological tissue 199 from the effects of the procedures describedherein associated with treatment using the tissue coagulation system200.

Placement of the energy directors described herein controls thedistribution of energy imparted to the target tissue. As such, theenergy director configurations described herein support approximatelyuniform energy distribution and/or current density, and thus moreuniform temperatures, through the target tissue volume. An example ofthis includes the use of RF energy where, for a number of energydirectors, and as described below, generally uniform energy distributionis obtained using relatively smaller spacing between the energydirectors toward the outside of a linear energy director array andrelatively larger spacing between the energy directors toward the centerof the energy director array. The spacing between the energy directorsis established and maintained using the energy director guide, adescription of which follows. An example of the tissue coagulationsystem 100 of an embodiment includes the InLine™ Bi-Polar RF LinearCoagulation System (also referred to as the InLine™ RadiofrequencyCoagulation device (“ILRFA”)) available from Resect Medical™ of Fremont,Calif.

FIGS. 2 and 3 are schematics of an energy director guide 102, includingvarious views, under an embodiment. The dimensions shown are in inches.The energy director guide 102 includes a support body having a linearseries of channels 202-212 that receive or carry the energy directors.The support body of an embodiment includes first and second end portionswith a surface extending between the first and second end portions. Thechannels 202-212 can also be referred to as orifices or openings, butare not so limited.

The energy director guide of various alternative embodiments can includea non-linear series of channels, and various combinations of a linearand a non-linear series of channels. The energy directors of anembodiment alternate in polarity or, alternatively, are in groups orsets that alternate in polarity, as described above, but the embodimentis not so limited. The configuration of the channels 202-212 in theguide supports delivery of an energy distribution or radiation patternin the tissue by the energy directors that provides sufficient and evencoagulation in the target tissue volume. Typically an coagulation widthin the range of approximately 0.5 cm to 1.5 cm is used to facilitate theresection, but the embodiment is not so limited. The energy directorguides include biocompatible materials like, for example, non-conductiveplastics like polycarbonate plastic, ULTEM® (polyetherimide), andAcrylonitrile Butadiene Styrene (“ABS”) plastic, but are not so limited.The energy director guides are manufactured using any of a number oftechniques and materials known in the art. For example, the energydirector guide of an embodiment can be formed using a single-piecemolded design. Further, the energy director guide of alternativeembodiments can be formed using two or more separate pieces assembled toform the guide using techniques known in the art.

While six (6) channels are shown for illustrative purposes, alternativeembodiments can include differing numbers of channels. One alternativeembodiment includes four (4) channels, while another alternativeembodiment includes eight (8) channels. The spacing among the channels202-212 varies according to the total number of energy directorsreceived in the energy director guide 102, as described further below.Generally, to account for electromagnetic coupling among the energydirectors when the energy directors are coupled to the generator, therelative spacing among the center-most channels (206 and 208 in thisembodiment) is largest while relative spacing among the end-mostchannels (202/204 and 210/212 in this embodiment) is smallest.

As described above, uniform energy distribution is important whengenerating an avascular volume of tissue suitable for bloodless ornear-bloodless resection. The energy director guide 102 described hereinprovides uniform energy distribution via the energy directors using achannel spacing, and consequently an energy director configuration, thataccounts for electromagnetic coupling effects among neighboring energydirectors. The energy director guide 102 of an embodiment includes six(6) channels 202-212 that, in operation, receive three (3) pairs ofbipolar energy directors. The spacing between channels 202 and 204 isapproximately 0.2995 inches. The spacing between channels 204 and 206 isapproximately 0.3285 inches. The spacing between channels 206 and 208 isapproximately 0.3937 inches. The spacing between channels 208 and 210 isapproximately 0.3285 inches. The spacing between channels 210 and 212 isapproximately 0.2995 inches.

The guide channel spacing that provides relatively uniform energydistribution is generated using resistive network models, but is not solimited. FIG. 4A shows a resistive network model 400 for an energydirector configuration including six (6) bipolar energy directors, underthe embodiment of FIGS. 2 and 3. Each of the six bipolar energydirectors is represented by one of nodes 1-6, wherein each node isassigned an alternating polarity 499, but the polarity assigned in thisexample is not limiting. The model 400 includes a number of resistorsR1-R19 coupled in various configurations among nodes 1-6 and currentsource 402, as described further below. The current source 402 isarbitrarily selected to produce 750 milliamps (“mA”) of current, but themodel is not so limited.

Generally, the resistor configurations of the model 400 simulate therelative power dissipation, including the coupling effects among thevarious combinations of alternating polarity nodes, in the tissuevolumes (“zones”) between the energy directors (nodes), as furtherdescribed below. Given that biological tissue has a resistivity(resistance per unit volume) that is proportional to the spacing betweenenergy directors, the resistor values of the model are iterativelyvaried to represent different channel spacing.

With reference to FIG. 4A, resistor R1 models the power dissipation inzone 1 as a result of current flowing between nodes 1 and 2. Likewise,resistors R2, R3, R4, and R5 each model the power dissipation as aresult of current flowing between the nodes that define each of zones2-5, respectively. The series combination of resistors R6, R7, and R8couple between nodes 1 and 4 and model the power dissipation acrosszones 1, 2, and 3 as a result of the current flowing between nodes 1 and4. The series combination of resistors R9, R10, and R11 couple betweennodes 3 and 6 and model the power dissipation across zones 3, 4, and 5as a result of the current flowing between these nodes. The seriescombination of resistors R12, R13, and R14 couple between nodes 2 and 5and model the power dissipation across zones 2, 3, and 4 as a result ofthe current flowing between nodes 2 and 5. Finally, the seriescombination of resistors R15, R16, R17, R18, and R19 couple betweennodes 1 and 6 and model the power dissipation across zones 1, 2, 3, 4,and 5 as a result of the current flowing between nodes 1 and 6. FIG. 4Bshows a table 450 including power dissipation values corresponding to anenergy director configuration providing balanced energy, under theembodiment of FIG. 4A.

FIG. 4C is a table 480 that includes power dissipation and spacinginformation corresponding to an energy director configuration providingbalanced energy, under the embodiment of FIG. 4A. This table 480includes total power dissipation 482 for each zone of the resistivenetwork model 400. The balanced energy director configuration usesnon-uniform channel spacing in the energy director guide to account forthe effects of electromagnetic coupling, as described above, under theembodiment of FIG. 2. In determining the total power dissipation perzone 482, the resistor values for the zones of an array are variediteratively until the total power dissipation per zone 482 isapproximately equal; the spacing per zone is proportional to theresistor values. The total power dissipation across zones 1-5 in abalanced energy director configuration is approximately 246 milliwatts(mW), 248 mW, 250 mW, 248 mW, and 246 mW, respectively, but is not solimited. Consequently, the power dissipation or distribution across thezones is approximately uniform.

Using the final values for the total power dissipation per zone 482,spacing ratios per zone 484 and 486 are generated. In an embodiment, twodifferent spacing ratios per zone 484 and 486 are generated, but theembodiment is not so limited. A first spacing ratio per zone 484references the spacing of the zones to the proximal-most/distal-mostzones (zones 1 and 5) of the array, and a second spacing ratio per zone486 references the spacing of the zones to the center zone (zone 3) ofthe array. Note, however, that the spacing ratios per zone can bereferenced to any zone of the array in alternative embodiments.

Using either of the spacing ratios per zone 484 and 486, the relativespacing among the channels is determined by assigning a referencespacing value to the reference zone (the zone for which the spacingration is one (1)). The spacing values for all other zones of the arrayare then each determined using the spacing ratio for each associatedzone as a multiplier against the reference spacing value. Referencespacing values are selected using techniques known in the art, whereinthe largest spacing value between the energy directors of an array isapproximately in the range of 0.75 cm to 2.00 cm, but the embodiment isnot so limited.

Alternative embodiments of the tissue coagulation system includediffering numbers of energy directors and, therefore, differing numbersof channels in the energy director guide. For example, one alternativeembodiment includes an energy director guide having a series of eight(8) channels that receive energy directors of alternating polarity. Asdescribed above, the channel spacing in this alternative embodiment isalso determined using a resistive network model simulation, but is notso limited.

FIG. 5A shows a resistive network model 500 for an energy directorconfiguration including eight (8) bipolar energy directors, under analternative embodiment. Extrapolating from the embodiment of FIG. 2, theenergy director guide of this example includes eight (8) channels, eachof which receive an energy director. Each of the eight bipolar energydirectors is represented by one of nodes 1-8, wherein each node isassigned an alternating polarity. The model 500 includes a number ofresistors R1-R44 coupled in various configurations among nodes 1-8 andcurrent source 502, as described further below. The current source 502is arbitrarily selected to produce one (1) amp of current, but the modelis not so limited.

Referring to FIG. 5A, resistor R1 models the power dissipation as aresult of current flowing between nodes 1 and 2. Likewise, resistors R2,R3, R4, R5, R6, and R7 each model the power dissipation as a result ofcurrent flowing between the nodes that define each of zones 2-7,respectively. The series combination of resistors R8, R9, and R10 couplebetween nodes 1 and 4 and model the power dissipation across zones 1, 2,and 3 as a result of the current flowing between nodes 1 and 4. Theseries combination of resistors R11, R12, R13, R14, and R15 couplebetween nodes 1 and 6 and model the power dissipation across zones 1, 2,3, 4, and 5 as a result of the current flowing between nodes 1 and 6.

Continuing, the series combination of resistors R16, R17, and R18 couplebetween nodes 3 and 6 and model the power dissipation across zones 3, 4,and 5 as a result of the current flowing between nodes 3 and 6. Theseries combination of resistors R19, R20, R21, R22, and R23 couplebetween nodes 3 and 8 and model the power dissipation across zones 3, 4,5, 6, and 7 as a result of the current flowing between nodes 3 and 8.The series combination of resistors R24, R25, and R26 couple betweennodes 2 and 5 and model the power dissipation across zones 2, 3, and 4as a result of the current flowing between nodes 2 and 5. The seriescombination of resistors R27, R28, and R29 couple between nodes 5 and 8and model the power dissipation across zones 5, 6, and 7 as a result ofthe current flowing between nodes 5 and 8.

Further, the series combination of resistors R30, R31, and R32 couplebetween nodes 4 and 7 and model the power dissipation across zones 4, 5,and 6 as a result of the current flowing between nodes 4 and 7. Theseries combination of resistors R33, R34, R35, R36, and R37 couplebetween nodes 2 and 7 and model the power dissipation across zones 2, 3,4, 5, and 6 as a result of the current flowing between nodes 2 and 7.Finally, the series combination of resistors R38, R39, R40, R41, R42,R43, and R44 couple between nodes 1 and 8 and model the powerdissipation across zones 1, 2, 3, 4, 5, 6, and 7 as a result of thecurrent flowing between nodes 1 and 8. FIG. 5B shows a table 550including power dissipation values corresponding to an energy directorconfiguration providing balanced energy, under the embodiment of FIG.5A.

FIG. 5C is a table 580 that includes power dissipation information 582and spacing information 584 and 586 corresponding to an energy directorconfiguration providing balanced energy, under the embodiment of FIG.5A. This power dissipation table 580 includes total power dissipation582 for each zone of the resistive network model 500. The balancedenergy director configuration uses non-uniform channel spacing in theenergy director guide to account for the effects of electromagneticcoupling, as described above. The total power dissipation across zones1-7 is approximately 563 mW, 565 mW, 564 mW, 567 mW, 564 mW, 565 mW, and563 mW, respectively. Consequently, the power dissipation ordistribution across the zones is approximately uniform.

The embodiments described above with reference to FIGS. 2, 3, 4, and 5provide approximately uniform power distribution among the tissue zonesof a target tissue volume. However, as power is proportional to theproduct of voltage and current, alternative embodiments of the energydirector array are configured to provide approximately uniform currentdensity through the target tissue volume. As such, the tissuecoagulation systems of various alternative embodiments generateavascular volumes of coagulated tissue using approximately uniformcurrent density. The energy director guide channel spacing that providesuniform current density is determined using resistive network models, asabove, but is not so limited.

The guide channel spacing that provides relatively uniform currentdensity is generated using resistive network models, but is not solimited. FIG. 6A shows a resistive network model 600 for an energydirector configuration including six (6) bipolar energy directors, underan alternative embodiment of FIGS. 2 and 3. Each of the six bipolarenergy directors is represented by one of nodes 1-6, wherein each nodeis assigned an alternating polarity. The model 600 includes a number ofresistors R1-R19 coupled in various configurations among nodes 1-6 andcurrent source 602, as described above with reference to FIG. 4A. Therelative power dissipation among the different zones is proportional tothe current density in the associated tissue zones. The current source602 is arbitrarily selected to produce 750 milliamps (“mA”) of current,but the model is not so limited. FIG. 6B shows a table 650 includingpower dissipation information corresponding to an energy directorconfiguration providing balanced energy, under the embodiment of FIG.6A.

FIG. 6C is a table 680 including current density and spacing informationcorresponding to an energy director configuration that provides balancedenergy, under the embodiment of FIG. 6A. This table 680 includes thecurrent density per zone 682 for the zones of the resistive networkmodel 600. The balanced energy director configuration uses non-uniformchannel spacing in the energy director guide to account for the effectsof electromagnetic coupling, as described above. In determining thecurrent density per zone 682, the resistor values for the zones of anarray are varied iteratively until the current density per zone 682 isapproximately equal; the channel spacing information is proportional toand derived from the final resistor values that provide approximatelyuniform current density. The current density per zone across zones 1-5is approximately 15.85 mA/spacing value, 15.8446 mA/spacing value,15.80769 mA/spacing value, 15.8446 mA/spacing value, and 15.85mA/spacing value, respectively, but is not so limited. Consequently, thecurrent density across the zones is approximately uniform.

Using the current density per zone 682, spacing ratios per zone 684 and686 are generated. In an embodiment, two different spacing ratios perzone 684 and 686 are generated, but the embodiment is not so limited. Afirst spacing ratio per zone 684 references the spacing of the zones tothe proximal-most/distal-most zones (zones 1 and 5) of the array, and asecond spacing ratio per zone 686 references the spacing of the zones tothe center zone (zone 3) of the array. Note, however, that the spacingratios per zone can be referenced to any zone of the array inalternative embodiments.

Using either of the spacing ratios per zone 684 and 686, the relativespacing among the channels is determined by assigning a referencespacing value to the reference zone (the zone for which the spacingration is one (1)). The spacing values for all other zones of the arrayare then each determined using the spacing ratio for each associatedzone as a multiplier against the reference spacing value. Referencespacing values are selected using techniques known in the art.

Alternative embodiments of the tissue coagulation system includediffering numbers of energy directors and, therefore, differing numbersof channels in the energy director guide. As described above, thechannel spacing in these alternative embodiments is also determinedusing a resistive network model simulation, but is not so limited.

FIG. 7 is a side view, end view, and top view of an energy directorguide 7000 and two or more pair of bipolar energy directors 7001-7006,under an alternative embodiment. The energy director guide 7000 supportsenergy director configurations that provide approximately uniform energydistribution and/or current density, and thus more uniform temperatures,through the target tissue volume. The energy director guide 7000configures the energy directors 7001-7006 in a linear row, and theenergy directors 7001-7006 alternate in polarity, where examplepolarities are shown, but the embodiment is not so limited. While threepairs of energy directors 7001-7002, 7003-7004, 7005-7006 are shown, theembodiment is not so limited.

The energy director guide 7000 supports generally uniform energydistribution in the target tissue using relatively smaller spacingbetween the energy directors of a pair and relatively larger spacingbetween the pairs of energy directors (also referred to as distinctpairs). For example, a first spacing is used between each of energydirectors 7001 and 7002, 7003 and 7004, and 7005 and 7006, while asecond spacing is used between energy directors 7002 and 7003, and 7004and 7005. In an embodiment, the spacing between the pairs of energydirectors is approximately 1.5 to 2 times the spacing between the energydirectors of a pair, but the embodiment is not so limited.

The configuration supported by the energy director guide 7000 results ina highly favored electrical path between the energy directors of thedistinct pairs. The favored electrical path results in a large portionof the electrical energy flowing between the energy directors of thedistinct pairs (between energy director pairs 7001/7002, 7003/7004, and7005/7006 in this example), thereby producing a coagulation in thetissue between the distinct pairs. Once the coagulation between thepairs is formed the impedance in this tissue begins to rise. As theimpedance rises, the alternate path to the opposite polarity energydirector in the adjacent distinct pair becomes more and more favorable(between energy directors 7002/7003 and 7004/7005 in this example). Astime progresses the impedance within the pairs (7002/7003 and 7004/7005)continues to increase resulting in the establishment of new pairs(7002/7003 and 7004/7005). This process continues until the entirecoagulation is complete.

The energy director guide of an alternative embodiment is reconfigurableto support a number of energy director configurations. For example, theenergy director guide can include channels that are moveable between anumber of pre-specified locations in the energy director guide so thatplacement of the channels in a first set of pre-specified locationsalong the guide supports the six energy guide configuration describedabove, and placement of the channels in a second set of pre-specifiedlocations along the guide supports the eight energy guide configurationdescribed above. Using this embodiment, a user can support manydifferent energy director configurations with a single energy directorguide.

Referring again to FIG. 1, the energy director guide of an embodimentindependently couples each of the energy directors to the generator viathe energy director guide. Further, the energy director guideindependently secures a position of each of the energy directors in thetarget tissue.

Regarding electrical coupling of the energy directors to the generator,the energy director guide of an embodiment uses direct electricalcoupling, while alternative embodiments use indirect electricalcoupling. FIG. 8 is a side view of an energy director guide 102 usingdirect coupling, under an embodiment. Each channel 202 and 204 of theguide 102 includes one or more contacts 702 and 704 that coupleconductors 706 and 708 of an energy conduit 799 from the generator (notshown) directly to the corresponding energy director 104 a and 104 b.When using bipolar energy directors, for example, a first conductor 706carrying signals of a first polarity couples to a first energy director104 a via a first contact 702. Likewise, a second conductor 708 carryingsignals of a second polarity couples to a second energy director 104 bvia a second contact 704. The contacts of an embodiment are fabricatedfrom materials with good spring and wear properties including, forexample, stainless steel and beryllium copper. Furthermore, the contactsof alternative embodiments can also secure or assist in securing aposition of the energy directors, but are not so limited.

FIG. 9 is a schematic of a circuit board 800 for use in an energydirector guide, under the embodiment of FIG. 2. The circuit board 800directly couples power signals having the appropriate polarity from apower source to the corresponding channels, and thus the correspondingenergy directors, via conducting traces 802 and 804. In the circuitboard 800 of an embodiment using alternating polarities, a firstconducting trace 802 carries an electrical signal having a firstpolarity, for example a positive polarity, among the energy directors ofchannels 202, 206, and 210. A second conducting trace 804 carries anelectrical signal having a second polarity, for example a negativepolarity, among the energy directors of channels 204, 208, and 212, butthe embodiment is not so limited.

In an embodiment using indirect coupling, a coil of electricallyconductive material that is insulated along its length is wound suchthat it forms a magnetic field around the electrically conductive energydirector thereby inducing a current flow in the energy director. FIG. 10is a side view of a guide 102 using indirect coupling, under anembodiment. Each channel 202 and 204 of the guide 102 includes a coil orwinding of conductive material 902 and 904 that indirectly couplesconductors 912 and 914 of an energy conduit 999 from the power source(not shown) to the corresponding energy director 104 a-104 b.

As described above, the energy director guide of an embodiment supportsindependent control of the position of the corresponding energydirectors. FIG. 11 shows a guide 102 that provides for independentcontrol of the deployment or insertion depth of each energy director1002, under an embodiment. The guide 102 provides independent control ofthe insertion of each energy director 1002 to independently variabledepths within the target tissue. Energy director deployment depths areapproximately in the range of one (1) centimeter to ten (10)centimeters, but are not so limited. As an example, the energy directordeployment depth of one embodiment is as much as approximately four (4)centimeters, while the energy director deployment depth of analternative embodiment is as much as approximately six (6) centimeters.Further, the energy directors of an embodiment include markings thatcorrespond to particular deployment depths for use as an aid duringinsertion of the energy directors in the target tissue.

The insertion of the energy directors 1002 can be performed individuallyor simultaneously as appropriate to the procedure. As such, each energydirector 1002 can be inserted into the target tissue to a differentdepth, thereby allowing the physician or clinician to avoid criticalanatomical structures with the application of RF energy. This isparticularly valuable since there often are present critical anatomicalstructures into which an energy director 1002 should not be inserted.Further, independent control of insertion depth for each energy director1002 supports the use of various visualization methods such asultrasound stenography, Computerized Tomography (“CT”), and MagneticResonance Imaging (“MRI”) in placement of the energy directors 1002 intarget tissue.

The independent control of the insertion depth also supports theuniformity of heating as follows. Large amounts of localized blood flowcan cause higher localized heat losses. These non-uniform heat lossescan result in uneven or incomplete coagulation. The tissue coagulationsystem of an embodiment counters this effect by supporting adjustment ofthe amount of energy conduit engagement around that region (e.g.,penetration depth). By doing this, the energy distribution can bealtered to account for the additional losses.

Alteration of the energy distribution is accomplished by decreasing thepenetration depth of the energy directors of the same polarity in anarea of tissue adjacent to the tissue containing the large localizedblood flow. This adjustment of penetration depth causes the impedancepath through these adjacent energy directors to increase, therebyshifting energy to the lower impedance path which has become the areathat includes the large blood flow. In the case of larger blood vessels,once they have been coagulated (as determined with the use of ultrasoundDoppler and/or a Doppler flow meter, for example), the energy conduitengagement can revert to a uniform amount as described above.

Once inserted into the target tissue, components of the energy directorguide exert enough force on the corresponding energy directors to securethem in the target tissue so that natural body movement will not pushthe energy directors out. The components of the energy director guideexert a retention force on the energy directors approximately in therange of 0.2 pound-force (“lbf”) to 2 lbf, but are not so limited.

FIG. 12 shows operation of the tissue coagulation system to generate anavascular volume of tissue, under the embodiment of FIG. 2. Generally,the coagulation procedure begins by positioning the energy directors1104 at a first depth in the target tissue 199. The depth shown isexemplary only, and is not a limiting depth. As such, the first depth atwhich the energy directors 1104 are placed is not limited to aparticular depth except by the length of the energy directors 1104 usedin a particular procedure or the anatomical structures present in thetarget tissue. Following placement of the energy directors, the userapplies power to the positioned energy directors 1104, thereby ablatingthe corresponding volume 1110 of engaged target tissue.

As another example in operation, the tissue coagulation system can beused to incrementally ablate a volume of target tissue as the energydirectors 1104 are incrementally advanced into the target tissue. FIG.13 shows operation of the tissue coagulation system to generate anavascular volume of tissue, under an alternative embodiment of FIG. 12.Referring to FIG. 13, and following coagulation of the tissue volume1110 associated with the first depth of the energy directors 1104 (FIG.12), the energy directors 1104 are further advanced to a second depth inthe target tissue 199. Following this advancement, the user couples thepower to the energy directors 1104, thereby ablating the correspondingincreased volume 1210 of engaged target tissue. Advancement of theenergy directors 1104 continues until the entire desired volume oftissue is rendered avascular or near-avascular. The shape and size ofthe coagulation volume 1110 and 1210 is controlled by the configurationof the electrode cluster, the geometry of the exposed energy directortips, the amount of power applied, the time duration that the power isapplied, and cooling of the electrodes, to name a few.

The tissue coagulation system provided herein along with the associatedmethods and procedures is particularly useful in controlling andoptimizing several critical parameters of a tissue coagulation procedureincluding energy density, thermal load from the surrounding tissue, andthe electrical impedance of the tissue. The tissue coagulation procedureincludes the thermal coagulation necrosis of soft tissues as an aidduring tissue resection. Methods of applying an amount of power orenergy in a balanced fashion using the tissue coagulation system tocreate a uniform section of coagulated tissue are provided below, wherethe power can be in any form that causes tissue to heat. The balancedfashion of power application is the delivery of power in such a way asto generate a reasonably uniform volume of coagulated tissue resultingin hemostasis. This is accomplished by generating a reasonably uniformtemperature increase in the target tissue.

The tissue coagulation system of an embodiment generates a uniformvolume of coagulated tissue that is a generally rectangular volume, butthe embodiment is not so limited. The rectangular volume can, forexample, have a width approximately in the range of 0.5 cm to 1 cm butis not so limited. The rectangular volume overcomes the problems inprior art tissue coagulation systems that might attempt to generateshaped coagulation planes/volumes using a series of sphericalcoagulation volumes.

As a result of their geometry, attempts to form a rectangularcoagulation plane using a series of overlapping spheres will result in avery irregular surface in the target tissue. This irregular surfacecauses problems when attempting to resect within such an irregular planeor surface of ablated tissue that was generated from a series ofspheres. If the spheres of ablated tissue are large enough to fullyinclude the desirable rectangular plane of ablated tissue, then too muchtissue will have been ablated. This excessive amount of dead tissue cansubsequently lead to significant and possibly life-threatening problemsfor the patient. If on the other hand, the coagulation spheres are sizedso that their maximum diameter is within the desirable rectangularplane, then a significant portion of the hemostasis is lost due to thelarge amount of unablated tissue that remains along the uneven edges ofthe overlapping spheres. In this case the reason for creating thecoagulation is largely reduced or eliminated. In addition, the use ofmonopolar energy to create the coagulation spheres, by the very natureof monopolar energy, results in a less defined and confined coagulationplane.

The typical approach of coagulating tissue by applying a uniform amountof power to a uniform volume of tissue is not the best solution becauseit does not result in a uniform increase in tissue temperature. Theproblems inherent in the typical systems and methods relate to severalissues. First, when the energy density is too low the thermal effectcannot be achieved. Likewise, when the thermal load from the surroundingtissue is too large the thermal effect will also not be achieved. Also,low electrical tissue impedance makes it difficult to heat since thedissipated power is proportional to the tissue impedance. Very low orhigh impedance will also be difficult for some power supplies to deliverthe required energy.

In one typical configuration known in the art, for example, severalenergy conduits can be placed within a target tissue at a uniformseparation. When an energy source such as radio frequency (RF) currentis uniformly applied in a bi-polar fashion to this arrangement of energyconduits, current flowing from the outer energy conduits distributesinward to the opposite polarity energy conduit. Similarly, currentflowing from the other energy conduits also flows to the oppositepolarity energy conduit. As can be shown and demonstrated, thisconfiguration results in a non-uniform overlapping of current flow. Thisuniform placement of energy conduits with a uniform amount of energydelivery does not therefore result in a uniform current distribution (orcurrent density), a uniform energy dissipation, or a uniform increase intemperature within the tissue.

The energy conduit configurations and methods provided by the tissuecoagulation system of an embodiment, however, provide more uniformtissue temperature in the target tissue, thereby reducing and/oreliminating many of these problems. FIG. 14 is a flow diagram 1400 foroperation of the tissue coagulation system, under an embodiment. Inoperation, and depending on the clinical conditions or requirements, auser selects an appropriate configuration of the electrodes, at block1402. This selection includes, for example, determinations as to thefollowing factors: (i) the number of electrodes in the cluster; (ii) therelative geometry, individual size, and tip exposure of the electrodes;(iii) the geometry of the target tissue region and identification of anytissue regions to be avoided; and (iv) the use of cooled or non-cooledelectrodes. Further, the selection can include processing image scandata from a CT scan, MRI, ultrasound, and/or other type of scanningdevice to determine the position of a targeted volume such as a tumorwithin the patient's body and the desired approach, placement, size, andnumber of electrodes.

The positioning of the electrodes in an embodiment is preplanned, forexample using a workstation, and the heat isotherms and coagulationvolume and time-course of the coagulation are determined. Based onhistorical or empirical information, the user may determine the desiredpower to be delivered to the tissue, the temperature as measured by theelectrode or measured elsewhere in the tissue by either integratedtemperature sensors in the energy directors or satellitetemperature-sensing electrodes, the desired time duration of heating,and the characteristics of impedance, to determine energy applicationtiming parameters and control against charring and other undesiredeffects.

Further, the selection of an electrode configuration under an embodimentincludes sizing of the electrodes based on the target organ. Forexample, the user can estimate a transverse dimension of the targetorgan. Using the estimated dimension, the user sizes the electrodesindividually or as a group so that the electrodes do not extend beyondthe target organ when fully inserted in the target organ.

Following the configuration and planning, the user positions the energydirector guide, and inserts the electrodes into the target tissue, atblock 1404. The electrodes can be placed individually or in unisonwithin the body tissue, as described herein. Real-time imaging can beused, for example CT, MRI, and/or ultrasound, during placement of theelectrodes to determine their proper position within a targeted volumeof tissue. The user inserts the electrodes to a desired depth.Additionally, if the electrodes are used with coolant, the user appliesthe coolant as appropriate.

During some procedures involving the tissue coagulation system the userseparates the target organ from one or more adjacent organs, but theembodiment is not so limited. This is done to prevent the electrodesfrom piercing the adjacent organs upon or during insertion into thetarget organ. Alternatively, the user can place a shield between thetarget organ and any adjacent organs to protect the adjacent organs frompenetration by the electrodes.

The user couples or applies power from the generator to the energydirector guide and the electrodes, at block 1406. Alternatively, thepower is coupled directly to the electrodes. While power is described inthis example, various alternative embodiments can, instead of usingpower as the controlling parameter, use current, voltage, impedance,temperature, time, and/or any combination of these, to control thetissue coagulation process. The power can be coupled to all of theelectrodes in unison, or sequentially in a predetermined sequence, asappropriate to the treatment procedure and/or the target tissue type.Likewise, the insertion depth of the electrodes and the amount of powercoupled to the electrodes is varied according to the treatment procedureand/or the target tissue type.

The application of power can be controlled automatically and/or manuallyunder any of a number of procedures, as described in detail below. Whenusing automatic control, the process is controlled according to one ormore algorithms or controllers integral to the generator system itselfor by one or more distributed algorithms and/or controllers coupledamong the components of the tissue coagulation system. Further, theapplication of power to the electrodes can be controlled in response toat least one parameter that includes time, temperature, impedance,and/or other known feedback parameters associated with the coagulationprocess.

The thermal coagulation of tissue is monitored, at block 1408, using thefeedback parameters appropriate to the equipment and procedure beingused. Coupling power to the energy director guide/electrodes, at block1406, results in generation of a plane of coagulated tissue in thetarget tissue, at block 1410. In an embodiment, pre-specified parametersand thresholds appropriate to the equipment and procedure are used todetermine when the plane of coagulated tissue has been generated. Theuser repeats various portions of the procedure, as appropriate to thetarget tissue, until a plane of coagulated tissue having the appropriatesize and shape is generated, at block 1412.

Operation of the tissue coagulation system of an embodiment includes theuse of a temperature feedback system in which temperature is measured atone or more locations within the tissue and the delivered power isvaried or altered (i.e., increased, decreased, or maintained) tomaintain the correct level of power delivery. Using this method, thetarget tissue is divided into quadrants or sections and the powerdelivery is individually varied on a section-by-section basis using thetemperature feedback information. When temperature within a givensection is increasing significantly beyond the other sections, the powerdelivery to that section is reduced sufficiently to maintain parity withthe other sections or to a pre-specified target temperature. Converselyif, based on the temperature feedback information, the temperature of asection is below that of other sections of the target tissue, the powerdelivered to that section is increased to achieve parity with the othersections or a pre-specified target temperature.

A predetermined rate of temperature increase can also be used to makethe temperature in the individual sections of the target tissuecomparable to resulting temperatures in other sections of the targettissue. For example, if the predetermined rate of temperature increaseis approximately in the range of 35 to 40 degrees Celsius per minute,then power would be applied at an initial rate and the increase intemperature would be evaluated. If as time progresses the temperature inthis individual section of target tissue is low, power to that sectionis increased. If the tissue temperature of a section of target tissue isincreasing beyond the predetermined rate, resulting in a hightemperature, the power delivery to that section is reduced. This methodhas the benefit of allowing a predetermined rate to be selected for aspecific tissue type and condition. Also, local variations in heat lossdue to the various factors such as blood flow are more readily accountedfor. In order to achieve a more uniform distribution, the number ofsections per unit of target tissue can be increased. Further, a moreuniform distribution can be achieved through the use of smallerpredetermined temperature ranges.

Operation of the tissue coagulation system of an embodiment alsoincludes the use of variations in an amount of tissue to which aquantity of power is applied. In this method the natural flow andoverlap of the delivered power is accounted for by increasing ordecreasing the spacing between the energy conduits. This effectivelyalters the energy path, thereby increasing or decreasing the relativeresistance and energy flow. This results in balanced power dissipationwithin the target tissue and, therefore, a uniform temperature rise. Asdescribed above, the spacing of the energy conduits in the tissue can bemodeled as an electrical circuit. This model assigns a resistance valueto the tissue between the energy conduits, which is proportional to thedistance between the energy conduits. Analyzing this circuit allows theresistance or distance between the energy conduits to be adjusted sothat a uniform amount of energy dissipation results within the tissueproviding a reasonably uniform increase in temperature, as describedabove with reference to FIGS. 4, 5, and 6.

Generally, procedures that use the tissue coagulation system of anembodiment begin with the selection of an energy conduit of asufficiently conductive material as appropriate to the power source. Theenergy conduit configuration should have a sufficient interface betweenthe energy conduits and the target tissue as appropriate for the desiredrate of power delivery and the resulting temperature rise sincetypically the point of highest energy density exists around the energyconduit.

An inadequate interface area between the energy conduit and the targettissue for the amount of delivered power can cause a rapid increase inthe desiccation and carbonization or char of the tissue around theenergy conduit, the result of which tends to inhibit or stop thetransfer of energy between the tissue and the energy conduit. Variousadditional methods can be used to help mitigate this limitation bylowering the temperature or temperature rise around the energy conduit.These mitigation methods include chilling the energy conduit or tissuearound the energy conduit, and/or adding an agent around the energyconduit to reduce the energy resistance between the energy conduit andthe target tissue resulting in a decrease in the power dissipationaround the energy conduit.

Following selection of the energy conduits, the energy conduits areplaced in a configuration that results in an approximately uniformtemperature increase sufficient to cause the targeted tissue tocoagulate. The number and size of energy conduits used is a function ofseveral factors including the available energy to be delivered from thepower source, the length of time for energy delivery, the desired shapeof the resulting coagulated tissue, the amount of heat loss within thetissue, and the susceptibility of the tissue to charring, to name a few.Once the electrodes are placed, the operator initiates power delivery tothe target tissue.

When using an power source that heats based on the electrical resistanceof the tissue, for example when using RF current, a lower amount ofpower is delivered in the initial stages of heating, but the embodimentis not so limited. The power initially delivered is approximately in therange of 10 to 100 Watts, depending on electrode deployment depth, butis not so limited because power values depend on the amount of interfacesurface area between the energy conduit and the tissue (for a relativelysmall interface surface area the amount of power can be significantlyreduced; likewise, the amount of power is increased for a relativelylarge interface surface area). This permits the cell membranes withinthe tissues and around the energy conduits to rupture and release theirelectrically conductive interstitial fluid. The release of theelectrically conductive interstitial fluids results in lower impedancearound the energy conduit and support subsequent delivery of largeramounts of power. This increase in power allows more power to bedelivered and shortens the process time. In addition, this larger amountof power permits larger blood vessels to be coagulated.

Upon initiating power delivery, the temperature of the target tissuebegins to rise. Factors such as local blood flow and dilatory effects inan area of the target tissue can result in an increased heat loss in thetarget tissue, thereby reducing the temperature rise within the tissueimmediately adjacent to that area. This condition is counteracted inoperation by increasing the amount of power delivered to the regioncontaining higher local blood flow by increasing the amount of energypassing through the target tissue of that effected region.

As energy within a particular region can be increased by reducing theamount of available energy conduits of like polarity in neighboringregions, partial retraction of the neighboring energy conduits of likepolarity, for example, decreases the tissue engagement surface area ofthose energy conduits, thereby redirecting a larger amount of energyinto the region of the higher local blood flow. The delivery of moreenergy into the region containing the higher local blood flowsubsequently offsets the additional heat loss. Once the unbalanced bloodflow has been removed, by coagulation of a single large blood vessel forexample, the energy conduits of the array are again placed withapproximately uniform exposure.

Completion of the coagulation process in target tissue is detected in anumber of ways, including the use of tissue temperature and/or tissueimpedance. When using tissue temperature, the tissue temperature can bemeasured in a number of ways. One way to measure tissue temperatureincludes measuring the temperature within or around the energy conduits.This measurement technique has the value of being easy to implementbecause it uses the energy conduit to house and deliver at least onetemperature sensor, without the need for additional materials.

The measurement of temperature via a sensor in the energy conduits,however, measures temperature in a location that is typically at or nearthe highest energy density; this tends to provide temperatures that arehigher than those measured within target tissue removed from theimmediate vicinity of the energy conduit. This issue is mitigatedsomewhat by using larger interfaces between energy conduits and targettissue, thereby reducing the high energy density around the energyconduit. This issue is also mitigated by, in the case of RF energy,using a bipolar energy conduit configuration. The bipolar configuration,because the energy conduits are local to the target tissue, maintainsmore of a “line of sight” energy dispersion resulting in a higher energydensity throughout the target tissue. This is in contrast to amono-polar arrangement in which a first polarity is used for the energyconduits local to the target tissue and a second (opposite) polarity isremotely located away from the target tissue; in this mono-polarconfiguration energy tends to dissipate outwardly from the energyconduits in all directions ultimately seeking the path of lowestresistance to the remote opposite polarity.

Another method for measuring tissue temperatures includes locating atemperature sensor within the target tissue, but remote to the energyconduits. This supports evaluation of temperatures in regions ofrelatively low energy density producing a lower or “worse case”temperature indication. Any effect of unusual heat loss such as fromlarge blood vessels can also be noted. The measurement of tissuetemperatures remote to the energy conduits includes using a fixedposition for temperature measurements away from the energy conduits, ormoving a temperature probe to various locations remote to the energyconduits during the procedure. Once temperatures within the targettissue reach a temperature above the tissue coagulation temperature(often at or above approximately 70 degrees Celsius) energy delivery isstopped.

Another method for determining the completion of the coagulation processincludes measuring the electrical impedance within the target tissue.With the application of coagulative energy to tissue, the electricalimpedance between the energy conduits and the tissue typically decreasesdue to release of the conductive interstitial fluid from the tissue.After this decrease in impedance, the impedance stabilizes and remainsso as the tissue increases in temperature. As energy delivery to thetissue is continued after coagulation has occurred, a higher degree oftissue desiccation occurs. This desiccation is indicated by a slowincrease in the impedance between the energy conduits. Therefore, thesmall continual increase in the tissue impedance denotes completion oftissue coagulation and the process of higher desiccation in the targettissue. Further application of energy results in a large and rapid riseof impedance denoting an unwanted transition from desiccation tocarbonization or char. Thus, once the steady increase in impedance isnoted energy delivery is stopped. It is assumed that the initialdelivery of energy to the target tissue was low enough to preventpremature tissue charring around the energy conduits only.

Another alternative method for determining the completion of thecoagulation process includes the use of temperature and tissue impedancemeasurements/measuring components. The temperature and tissue impedancemeasuring components are in a single feedback system, but the embodimentis not so limited.

Once coagulation is complete in the target tissue, the energy conduitsare removed. The energy conduits are relocated to another area of targettissue and the above methods are repeated as necessary to form largerplanes of coagulated tissue, as described herein. If the coagulationmethod uses bipolar RF energy, then one of the outer most energyconduits should be located directly adjacent to the coagulation createdby the previous coagulation plane, but the embodiment is not so limited.Once the full length of the coagulated coagulation plane is completed,tissue resection through the coagulated plane is performed.

Various alternative embodiments can simultaneously use any number ofenergy director guides/electrodes in a procedure in order to formvolumes of coagulated tissue having shapes and sizes appropriate to thetreatment procedure. Numerous alternatives would be recognized by thoseskilled in the art in view of the tissue coagulation system describedherein.

As described above, the application of power under an embodiment iscontrolled automatically and/or manually under a number of procedures. Afirst type of procedure uses a predetermined pattern of energy deliveryaccording to a time schedule. A second type of procedure varies theapplication of energy to the target tissue volume in accordance withtemperature information or feedback parameters of the tissue. A thirdtype of procedure varies the application of energy to the target tissuevolume in accordance with impedance information or feedback parametersof the tissue in combination with elapsed time. A fourth type ofprocedure varies the application of energy to the target tissue volumein accordance with impedance information or feedback parameters of thetissue. A fifth type of procedure varies the application of energy tothe target tissue volume in accordance with temperature and impedanceinformation or feedback parameters of the tissue. Each of theseprocedure types is described in detail below.

The first type of procedure uses a predetermined pattern of energydelivery according to a time schedule. One procedure under this firstprocedure type directs the user to select a predetermined power settingin accordance with a deployment depth of one or more of the electrodesin the target tissue, and then directs application of the power for apredetermined period of time. The procedure directs selection of a 15Watt (W) power setting for a 1 centimeter (“cm”) electrode deploymentdepth, a 30 W power setting for a 2 cm electrode deployment depth, a 45W power setting for a 3 cm electrode deployment depth, a 60 W powersetting for a 4 cm electrode deployment depth, a 75 W power setting fora 5 cm electrode deployment depth, and an 85 W power setting for a 6 cmelectrode deployment depth. Following selection of a power settingappropriate to the electrode deployment depth, the procedure directsapplication of power for a period not to exceed approximately threeminutes. Upon the expiration of the three minute period, the user fullyretracts the electrodes and removes the tissue coagulation device. Theprocess is repeated as appropriate to generate the desired volume ofablated tissue. This pattern of energy delivery may be used with theInLine™ Radiofrequency Coagulation device described above and a RadioTherapeutics Corporation (Boston Scientific) Generator (Models RF 2000™or RF 3000™ with cable adaptor Reorder Number 03-0504-U) for example,but is not so limited.

Another procedure under this first procedure type directs the user toapply predetermined amounts of power according to a time schedule and adeployment depth of one or more of the electrodes in the target tissue.As an example, for a 1 cm electrode deployment depth, the proceduredirects application of 10 Watts of power for 90 seconds (“secs”),followed immediately by application of 15 Watts of power for 60 seconds,followed immediately by application of 20 Watts of power for 30 seconds.When using a 2 cm electrode deployment depth, the procedure directsapplication of 25 Watts of power for 90 seconds, followed immediately byapplication of 30 Watts of power for 60 seconds, followed immediately byapplication of 35 Watts of power for 30 seconds. When using a 3 cmelectrode deployment depth, the procedure directs application of 40Watts of power for 90 seconds, followed immediately by application of 45Watts of power for 60 seconds, followed immediately by application of 50Watts of power for 30 seconds. When using a 4 cm electrode deploymentdepth, the procedure directs application of 55 Watts of power for 90seconds, followed immediately by application of 60 Watts of power for 60seconds, followed immediately by application of 65 Watts of power for 30seconds. When using a 5 cm electrode deployment depth, the proceduredirects application of 70 Watts of power for 90 seconds, followedimmediately by application of 75 Watts of power for 60 seconds, followedimmediately by application of 80 Watts of power for 30 seconds. Whenusing a 6 cm electrode deployment depth, the procedure directsapplication of 80 Watts of power for 90 seconds, followed immediately byapplication of 85 Watts of power for 60 seconds, followed immediately byapplication of 90 Watts of power for 30 seconds. Upon completion of thethree power cycles appropriate to the deployment depth, the user fullyretracts the electrodes and removes the tissue coagulation device. Theprocess is repeated as appropriate to generate the desired volume ofablated tissue.

Yet another procedure under this first procedure type directs the userto apply predetermined amounts of power according to a time schedule anda deployment depth of one or more of the electrodes in the targettissue. As an example, for a 1 cm electrode deployment depth, theprocedure directs application of 13 Watts of power for 90 seconds(“secs”), followed immediately by application of 15 Watts of power for60 seconds, followed immediately by application of 17 Watts of power for30 seconds. When using a 2 cm electrode deployment depth, the proceduredirects application of 27 Watts of power for 90 seconds, followedimmediately by application of 30 Watts of power for 60 seconds, followedimmediately by application of 33 Watts of power for 30 seconds. Whenusing a 3 cm electrode deployment depth, the procedure directsapplication of 41 Watts of power for 90 seconds, followed immediately byapplication of 45 Watts of power for 60 seconds, followed immediately byapplication of 50 Watts of power for 30 seconds. When using a 4 cmelectrode deployment depth, the procedure directs application of 54Watts of power for 90 seconds, followed immediately by application of 60Watts of power for 60 seconds, followed immediately by application of 66Watts of power for 30 seconds. When using a 5 cm electrode deploymentdepth, the procedure directs application of 68 Watts of power for 90seconds, followed immediately by application of 75 Watts of power for 60seconds, followed immediately by application of 83 Watts of power for 30seconds. When using a 6 cm electrode deployment depth, the proceduredirects application of 77 Watts of power for 90 seconds, followedimmediately by application of 85 Watts of power for 60 seconds, followedimmediately by application of 94 Watts of power for 30 seconds. Uponcompletion of the three power cycles appropriate to the deploymentdepth, the user fully retracts the electrodes and removes the tissuecoagulation device. The process is repeated as appropriate to generatethe desired volume of ablated tissue. This pattern of energy deliverymay be used with the InLine™ Radiofrequency Coagulation device describedabove and a RITA® System RF Generator (Model 1500 with cable adaptorReorder Number 03-0501-U or Model 1500X with cable adaptor ReorderNumber 03-0502-U) for example, but is not so limited. This pattern ofenergy delivery may also be used with a Radionics® (Tyco Healthcare)Cool-tip™ RF Generator (with cable adaptor Reorder Number 03-0503-U).

These procedures under which the user applies predetermined amounts ofpower according to a time schedule and an electrode deployment depth areeffective in coagulating many types of tissue. The staged power deliveryresults in delivery of smaller amounts of power at the beginning of theprocedure, where the smaller amounts of power coagulate tissue havinglower blood flow, for example cirrhotic tissue and fatty tissue, earlierin the procedure without flashing effects that could stop thecoagulation procedure. Furthermore, the delivery of higher amounts ofpower later in the procedure thoroughly coagulate tissue having higherblood flows without unduly prolonging the total time of the procedure.

The second type of procedure varies the application of energy to thetarget tissue volume in accordance with temperature information orfeedback parameters of the tissue. This procedure includes variations inthe amount of energy and/or time of energy application based ontemperature information received from at least one temperature sensor inthe target tissue. The amount of energy and/or time of energyapplication are controlled in accordance with pre-specified temperatureparameters appropriate to the target tissue type/procedure to preventthe delivery of excess energy and consequently prevents overheating andcharring of the target tissue.

FIG. 15 is a flow diagram 1500 for controlling tissue coagulation inaccordance with temperature parameters, under an embodiment. Followingplacement of the electrodes in the target tissue, the user increases thepower delivered to the target tissue by an amount P₁, at block 1502,where P₁ is approximately in the range 0.1 W/sec to 10 W/sec. Adetermination is made whether rates of temperature change in the targettissue are less than or equal to I_(min), at block 1504, where I_(min)is approximately in the range 0.1 degrees Celsius/sec to 5 degreesCelsius/sec. When rates of temperature change are less than I_(min), thepower delivered to the target tissue is increased, at block 1506, andoperation continues at block 1504.

When rates of temperature change are greater then I_(min), adetermination is made whether rates of temperature change in the targettissue are greater than or equal to I_(max), at block 1508, whereI_(max) is approximately 5 degrees Celsius/sec. When rates oftemperature change are greater than I_(max), the power delivered to thetarget tissue is decreased, at block 1510, and operation continues atblock 1504.

When rates of temperature change in the target tissue are within therange bounded by I_(min) and I_(max), a determination is made whether atemperature of the target tissue is greater than T_(max), at block 1512,where T_(max) is approximately in the range 85 to 115 degrees Celsius.When a temperature of the target tissue is greater than T_(max), thepower delivered to the target tissue is decreased, at block 1514, andoperation continues at block 1504.

When the rates of temperature change in the target tissue are within therange bounded by I_(min) and I_(max) and the temperature of the targettissue is less than T_(max), the power delivered to the target tissue isincreased by an amount P₂, at block 1516, where P₂ is approximately inthe range 0.1 W/sec to 10 W/sec. Operation continues at block 1518 wherea determination is made whether the elapsed time of power application tothe target tissue exceeds D_(max), where D_(max) is a pre-specifiedamount of time greater than one (1) minute. When the elapsed timeexceeds D_(max), the application of power to the target tissue isterminated, at block 1520; otherwise, operation continues at block 1504as described above.

An example procedure that controls tissue coagulation in accordance withtemperature parameters, as described above, uses the following parametervalues: P₁ is approximately 2 W/sec; I_(min) is approximately 2 degreesCelsius/sec; I_(max) is approximately 5 degrees Celsius/sec; T_(max) isapproximately 105 degrees Celsius; P₂ is approximately 4 W/sec; andD_(max) is approximately 3 minutes. These parameters are examples onlyand do not limit the embodiments described herein.

When controlling coagulation using temperature information, thetemperature is increased at an appropriate rate, for example a rateapproximately in the range 25 degrees Celsius/minute to 100 degreesCelsius/minute to a temperature endpoint in the target tissue. Thetemperature endpoint of an embodiment is approximately in the range of55 degrees Celsius to 110 degrees Celsius, but is not so limited. Theuse of an appropriate rise in tissue temperature around an electroderesults in release of the highly conductive fluid inside cells of thetarget tissue. This fluid release lowers the impedance around theelectrode helping to prevent charring and allowing the continued (orincreasing) flow of energy to the target tissue. This release is causedby the thermal damage to the cell wall. If the energy rise is too quick,the fluid will be quickly boiled or flashed off; this results in nosignificant benefit and helps to increase the tendency for tissuecharring and a loss of ability to deliver energy to the target tissue.

The third type of procedure varies the application of energy to thetarget tissue volume in accordance with impedance information orfeedback parameters of the tissue in combination with elapsed time.Generally, this type of procedure applies power to the target tissueaccording to pre-established time schedules and in accordance withchanges in impedance and an amount of electrode engagement with thetarget tissue (engaged surface area of electrodes is a function ofelectrode size and electrode deployment depth).

FIG. 16 is a flow diagram 1600 for controlling tissue coagulation inaccordance with impedance and time parameters, under an embodiment.Following placement of the electrodes in the target tissue, the userincreases the power delivered to the target tissue by an amount P₁, atblock 1602, where P₁ is approximately in the range 0.1 W/sec to 10W/sec. A determination is made whether the elapsed time is greater thanT₁, at block 1604, where T₁ is approximately in the range 1 second to100 seconds.

When the elapsed time exceeds T₁, a determination is made whether animpedance of the target tissue is greater than an amount I_(max), atblock 1608, where I_(max) is approximately in the range 1 Ohm to 200Ohms. When the impedance exceeds I_(max), the application of power tothe target tissue is terminated, at block 1612; otherwise, operationcontinues at block 1602 as described above.

When the elapsed time does not exceed T₁, as determined at block 1604, adetermination is made whether the impedance of the target tissue isdecreasing, at block 1606. If the impedance is not decreasing, thenoperation continues at block 1602, as described above. If the impedanceis increasing, then the application of power to the target tissue ismaintained, at block 1610, and operation continues at block 1608 where adetermination is made as to whether impedance of the target tissue isgreater than an amount I_(max). When the impedance exceeds I_(max), theapplication of power to the target tissue is terminated, at block 1612;otherwise, operation continues at block 1602 as described above.

An example procedure that controls tissue coagulation in accordance withimpedance parameters, as described above, uses the following parametervalues: P₁ is approximately 2 W/sec; T₁ is approximately 15 seconds; andI_(max) is approximately 50 Ohms. These parameters are examples only anddo not limit the embodiments described herein.

The fourth type of procedure varies the application of power to thetarget tissue volume in accordance with impedance information orfeedback parameters of the tissue. Generally, this type of procedureapplies power to the target tissue in accordance with changes inimpedance and an amount of electrode engagement with the target tissue(engaged surface area of electrodes is a function of electrode size andelectrode deployment depth). As an example, power is applied in oneembodiment until the impedance of the target tissue begins to drop. Asthe impedance begins to drop, the power level is stabilized at anapproximately constant level until the impedance stabilizes. Once theimpedance stabilizes, the power level is increased to a predeterminedlevel and held until the impedance begins to increase. As the impedancebegins to increase, the power level can be gradually decreased in orderto maintain or prolong the duration of the impedance rise.

As another example, power is applied until the impedance of the targettissue begins to drop. As the impedance begins to drop, the power levelis stabilized at an approximately constant level until the impedancestabilizes. Once the impedance stabilizes, the power level is graduallyincreased until such time as the impedance begins to increase. A maximumpower level can be specified, but the embodiment is not so limited. Asthe impedance begins to increase, the power level can be graduallydecreased in order to maintain or prolong the duration of the impedancerise.

FIG. 17 is a flow diagram 1700 for controlling tissue coagulation inaccordance with impedance parameters, under an embodiment. Followingplacement of the electrodes in the target tissue, an initial impedancelevel I_(initial) is set, at block 1702, where I_(initial) is selectedor determined according to the tissue type of the target tissue. Thepower delivered to the target tissue is then increased by an amount P₁,at block 1704, where P₁ is approximately in the range 0.1 W/sec to 10W/sec. A determination is made whether the initial impedance levelI_(initial) has decreased more than an amount I_(low1), at block 1706,where I_(low1) is approximately in the range 0.1 Ohms to 5 Ohms. If theinitial impedance level I_(initial) has not decreased more thanI_(low1), the power delivered to the target tissue is increased by anamount P₂, at block 1708, where P₂ is approximately in the range 0.1W/sec to 10 W/sec, and operation continues at block 1706 as describedabove.

If the initial impedance level I_(initial) has decreased more thanI_(low1), the power delivered to the target tissue is stabilized andmaintained at the current level, at block 1710. The decreased impedanceof the target tissue is set and defined as a value I_(dropping), atblock 1712. The impedance level I_(dropping) is then monitored fordecreases that exceed impedance level I_(low2), at block 1714, whereI_(low2) is approximately in the range 1 Ohm to 20 Ohms. If theimpedance level I_(dropping) has decreased more than I_(low2), operationcontinues at block 1710, where the power delivered to the target tissueis maintained and operation continues as described above.

If the impedance level I_(dropping) has not decreased more thanI_(low2), the power delivered to the target tissue is increased by anamount P₃, at block 1716, where P₃ is approximately in the range 0.1W/sec to 10 W/sec. A determination is then made whether the amount ofpower delivered to the target tissue is equal to or greater than anamount P_(max), at block 1718. The power level P_(max) of an embodimentis determined from a lookup table in response to at least one parameterthat includes target tissue type, initial impedance level I_(initial),electrode size, and electrode deployment depth, but is not so limited.Alternatively, P_(max) is pre-specified and preset in accordance with atleast one parameter that includes target tissue type, initial impedancelevel I_(initial), electrode size, and electrode deployment depth, butis not so limited. If the current power level is less than P_(max) thenthe power delivered to the target tissue is increased by an amount P₃,at block 1716, and operation continues as described above.

If the power level is equal to or greater than P_(max), at block 1718,the power level is maintained, at block 1720. The impedance levelI_(dropping) is then monitored for increases that exceed an amountI_(high1), at block 1722. Impedance level I_(high1) of an embodiment isapproximately equal to or greater than two times impedance levelI_(initial), but is not so limited. If the change in impedance levelI_(dropping) does not exceed I_(high1), a determination is made whetherthe level of power delivered to the target tissue is equal to or greaterthan an amount P_(max), at block 1718, and operation continues asdescribed above. If the change in impedance level I_(dropping) exceedsI_(high1), however, the application of power to the target tissue isterminated, at block 1724.

An example procedure that controls tissue coagulation in accordance withimpedance parameters, as described above, uses the following parametervalues: P₁ is approximately 2 W/sec; P₂ is approximately 4 W/sec;I_(low1) is approximately 1 Ohm; and I_(low2) is approximately 1 Ohm.Alternatively, power levels P₁, P₂, and P₃ can be equal, but are not solimited. These parameters are examples only and do not limit theembodiments described herein.

FIG. 18 is a plot 1800 of impedance (Impd (Ohms)) 1802 and power (Pwr(W)) 1804 (y-axis) versus time (Time (min)) (x-axis) for use incontrolling tissue coagulation, under an embodiment. In the followingdescription, the impedance curve 1802 includes Regions 1, 2, 3, 5, 6, 9,10, and 12, while the power curve 1804 includes Regions 4, 7, 8, 11, and13. This plot 1800 generally represents the impedance 1802 and power1804 during a tissue coagulation procedure using the tissue coagulationsystem of an embodiment under impedance control. This plot 1800 cangenerally be used in at least one of manual, automatic, and combinationautomatic/manual control of the tissue coagulation system of anembodiment. This plot 1800 is an example only and does not limit theembodiments described herein.

The plot 1800 was derived using an electrode deployment depth in thetarget tissue of approximately four to five centimeters, but is not solimited. A decrease in the electrode deployment depth, for example,would shift the impedance 1802 curve up and the power 1804 curve downrelative to values on the y-axis. Further, different types of targettissue can shift the impedance 1802 and power 1804 curves up or down.Moreover, electrodes of different sizes can change a shape of theimpedance curve 1802 where, generally, larger electrodes result in moregradual changes in the impedance curve relative to smaller electrodes.

Procedures that use the tissue coagulation system of an embodiment beginwith placement/deployment of the electrodes into the target tissue bythe user. Using standard surgical techniques, the user determines theappropriate resection plane to be used. All electrodes of the device areretracted, and the device is placed in contact with the patient suchthat all electrodes are properly positioned for deployment into theintended tissue. The electrodes are then deployed into the target tissueusing imaging guidance as appropriate. Region 1 of the plot 1800generally represents the decreasing impedance resulting from electrodeplacement/deployment in the target tissue. Region 2 generally representsthe impedance as it stabilizes during/after final electrode placement inthe target tissue. Region 3 generally represents stable impedancefollowing electrode placement in the target tissue.

Following placement of the electrodes in the target tissue andstabilization of the impedance, power is applied to the target tissuevia the deployed electrodes as described above. Region 4 generallyrepresents the point at which the tissue coagulation system appliespower to the target tissue. Region 5 generally represents the decreasingimpedance in the target tissue that arises as a result of theapplication of power. The decreasing impedance results as theapplication of power causes cell membranes in the target tissue to meltor rupture and release conductive fluid into the area of the electrodes.Region 6 generally represents stabilized impedance in the target tissuefollowing the initial application of power by the tissue coagulationsystem.

Once the impedance has stabilized in the target tissue, the tissuecoagulation system increases the power applied to the target tissue. Thepower can be increased according to any number of procedures, includingincreasing in step-wise fashion, increasing linearly to a pre-specifiedmaximum level, increasing in an exponential fashion, and increasinguntil a pre-specified temperature is reached in the target tissue, toname a few. Region 7 generally represents an increase in power appliedto the target tissue, and Region 8 generally represents a maximum powerlevel to which the power is increased. Region 9 generally representsstabilized impedance in the target tissue during/following the increasedapplication of power by the tissue coagulation system.

Desiccation of the target tissue occurs as a result of the power appliedto the tissue (Regions 7 and 8 of the plot). Desiccation of the targettissue generally results in an increase in the impedance of the targettissue, where the rate of increase in impedance is controlled inresponse to the level of applied power. Region 10 generally representsthe onset of increasing impedance in the target tissue as a result oftissue desiccation. Region 11 generally represents a reduction rate ofthe power applied to the target tissue in response to the increasingimpedance, while area 12 generally represents the corresponding rate ofincrease of the impedance in the target tissue.

The tissue coagulation system, under automatic and/or manual control,reduces the power applied to the target tissue at any of a number ofrates in order to control the rate at which the impedance rises. Forexample, increasing the rate at which the power is reduced (increasingslope of Region 11) results in a slower increase in the impedance(decreasing slope of Region 12). Likewise, decreasing the rate at whichthe power is reduced (decreasing slope of Region 11) results in a fasterincrease in the impedance (increasing slope of Region 12). Rates ofpower reduction are specified as appropriate to a tissue type of thetarget tissue and/or a user, but are not so limited.

Region 13 generally represents termination of the application of powerto the target tissue and, therefore, termination of the coagulationprocedure.

Turning to the fifth type of procedure, this procedure varies theapplication of energy to the target tissue volume in accordance withtemperature and impedance information or feedback parameters of thetarget tissue. Generally, this type of procedure applies power to thetarget tissue in accordance with changes in temperature and impedance inthe target tissue. The impedance changes relate to an amount ofelectrode engagement with the target tissue (engaged surface area ofelectrodes is a function of electrode size and electrode deploymentdepth), but are not so limited.

As an example, power is applied in one embodiment until the impedance ofthe target tissue begins to decrease. As the impedance decreases, thepower level is stabilized at an approximately constant level until theimpedance stabilizes. Once the impedance stabilizes, the power level isincreased according to a predetermined slope. When a pre-specifiedtarget temperature is reached in the target tissue, the power level isaltered as appropriate to the configuration of the coagulation volume soas to maintain the target temperature until such time as the impedanceincreases to a pre-specified target impedance. In an alternativeprocedure, when a pre-specified target temperature is reached in thetarget tissue, the power level is altered so as to maintain the targettemperature until such time as the impedance increases at apre-specified rate of increase.

FIG. 19 is a plot 1900 of time verses impedance depicting an effectivetissue coagulation cycle using the tissue coagulation system, under anembodiment. During this cycle the impedance decreases as the amount ofelectrical interface between the electrode(s) and tissue increases(“Electrode Placement” portion of plot 1900). The impedance thenstabilizes with the finial placement of the electrode(s) in relation tothe tissue (“Initial Impedance” portion of plot 1900). The impedancefurther decreases as sufficient energy is applied causing release of theinterstitial fluid (“Impedance Drop” portion of plot 1900), followed bya relatively steady or constant impedance as the tissue temperaturecontinues to rise (“Steady Impedance” portion of plot 1900). Therelatively steady impedance gives way to a slow increase in impedance asthe tissue desiccation becomes more significant (“Impedance Rise—TissueDesiccation” portion of plot 1900).

FIG. 20 is a plot 2000 of time verses impedance depicting an undesirabletissue coagulation cycle in which the amount of applied power is too lowfor the amount of tissue being treated using the tissue coagulationsystem, under an embodiment. Similar to plot 1900 described above,during this cycle 2000 the impedance decreases as the amount ofelectrical interface between the electrode(s) and tissue increases(“Electrode Placement” portion of plot 2000), stabilizes with the finialplacement of the electrode(s) in relation to the tissue (“InitialImpedance” portion of plot 2000), further decreases as sufficient energyis applied causing release of the interstitial fluid (“Impedance Drop”portion of plot 2000), followed by a relatively constant impedance asthe tissue temperature continues to rise (“Steady Impedance” portion ofplot 2000). However, at the end of the cycle the impedance does notincrease with the completion of the cycle (“Cycle Ended”). As a resultof an inadequate amount of delivered power the tissue has not been fullydesiccated resulting in little or no hemostasis.

FIG. 21 is a plot 2100 of time verses impedance depicting an undesirabletissue coagulation cycle in which the amount of applied power is toohigh for the amount of tissue being treated using the tissue coagulationsystem, under an embodiment. Similarly to plot 1900 described above,during this cycle 2100 the impedance decreases as the amount ofelectrical interface between the electrode(s) and tissue increases(“Electrode Placement” portion of plot 2100), stabilizes with the finialplacement of the electrode(s) in relation to the tissue (“InitialImpedance” portion of plot 2100), further decreases as sufficient energyis applied causing release of the interstitial fluid (“Impedance Drop”portion of plot 2100), followed by a relatively constant impedance asthe tissue temperature continues to rise (“Steady Impedance” portion ofplot 2100). However, before the end of the cycle the impedance rapidlyincreases (“Rapid Impedance Rise” portion of plot 2100). The rapidincrease in impedance results in a relatively large tissue impedancevalue terminating the cycle (“Cycle Ended” portion of plot 2100). Theexcess amount of delivered power to the target tissue therefore resultsin incomplete coagulation of the target tissue.

FIG. 22 is a flow chart 2200 of an automatic control cycle in whichparameters of the power delivered to tissue using the tissue coagulationsystem are controlled as a function of various tissue types, impedances,amounts of tissue to be treated, and cycle duration, under anembodiment. The parameters of the power delivered include at least oneof the amount of power delivered to the tissue, the rate at which thepower is delivered to the tissue, the duration of the power delivery, aswell as the timing of the power delivery, but the embodiment is not solimited.

The control cycle 2200 begins with all variables being initialized, atblock 2201. An impedance measurement is made, at block 2202, and themeasured impedance is compared to the previous impedance values, in thiscase the initialized values. The measured impedance is compared to apredetermined minimum impedance value “IL”, at block 2203. If themeasured impedance is not stable and/or not greater than the value IL,operation returns to block 2250 where the measurement and value testsare repeated as described above with reference to blocks 2202 and 2203.This operation is typical during the “Electrode Placement” portion of aprocedure as noted in plots 1900, 2000, and 2100 described above. Whenthe measured impedance is stable and greater than the value IL, at block2203, operation continues to determine if user input has been satisfiedto begin the application of energy, at block 2204. If user input has notbeen satisfied, operation returns to block 2250 where the measurementand value tests are repeated, as described above with reference toblocks 2202 and 2203.

When the user input is satisfied, at block 2204, energy is applied tothe target tissue at a predetermined power level that is set ordetermined relative to the value of the stable impedance (measured atblock 2203), at block 2205. This in part accounts for both the amountand type of target tissue being treated. Higher impedance levels requirea relatively lower amount of energy as compared to lower impedancelevels which denote, among other things, larger amounts of tissue to betreated requiring larger amounts of delivered energy. This portion ofthe flow chart corresponds to the “Initial Impedance” and “PowerApplied” portions of plots 1900, 2000, and 2100 as described above.

With the application of energy at the preset power level, anotherimpedance measurement is made, at block 2206, and this second impedancemeasurement is compared to the first impedance value previouslymeasured, at block 2202. When the comparison of the first and secondimpedance values indicates the impedance is not changing, then theapplied energy or power is increased by N1%, at block 2208, andoperation returns to repeat the impedance measurement and comparison, atblocks 2206 and 2207. When the comparison of the first and secondimpedance values indicates the impedance is increasing, then the poweris reduced and reapplied at rate R1 to a level L1% that is less than theprevious level, at block 2209; operation then returns to repeat theimpedance measurement and comparison, at blocks 2206 and 2207.

When the comparison of the first and second impedance values indicatesthe impedance is neither stable nor increasing, at block 2207, adetermination is made the impedance is decreasing, at block 2210. Thelevel of the applied power is held at a constant level in response tothe decreasing impedance, at block 2211. This portion of the flow chartcorresponds to the “Impedance Drop” portion of plots 1900, 2000, and2100 as described above.

The impedance is measured a third time, at block 2212, and adetermination is made whether the measured impedance continues todecrease, at block 2213. When the comparison of the previously measuredimpedance values indicates the impedance is decreasing, at block 2213,operation returns to hold the applied power at a constant level andrepeat the impedance measurement and comparison, at blocks 2211 and2212.

When comparison of the previously measured impedance values indicatesthe impedance is not decreasing, at block 2213, the impedance ismeasured a fourth time, at block 2214, and this fourth impedancemeasurement is compared to one or more of the previous three impedancemeasurements, at block 2215. When the comparison of the impedancemeasurements indicates the impedance is not increasing, indicating theimpedance has stabilized, the power is increased by N2%, at block 2216,and operation returns to repeat the impedance measurement andcomparison, at blocks 2214 and 2215. This portion of the flow chartcorresponds to the “Steady Impedance” portion of plots 1900, 2000, and2100 as described above. This increase in power helps prevent theoccurrence described above with reference to plot 2000 without causingthe end condition described above with reference to plot 2100.

When the comparison of the impedance measurements (block 2215) indicatesthe impedance is increasing, a comparison is made regarding the percentof cycle completion, at block 2217. The comparison of the percent ofcycle completion is made by comparing an elapsed time of the controlcycle against a pre-specified amount of time, but the embodiment is notso limited. If the cycle completion exceeds approximately 100%, themeasured impedance is compared to a predetermined high impedance value“IH”, at block 2218. If the measured impedance exceeds the value IH, thecycle is completed and the application of power to the target tissue isterminated, at block 2219. This portion of the flow chart corresponds tothe “Cycle Complete” portion of plots 1900, 2000, and 2100 as describedabove. If the measured impedance does not exceed the value IH (block2218), operation returns to repeat the measurement and comparison asdescribed above with reference to blocks 2214 and 2215.

If however the cycle completion does not exceed approximately 100%, asdetermined by the comparison at block 2217, the measured impedancevalues are evaluated and an impedance increase rate is determined. Theimpedance increase rate is compared to a first predetermined impedanceincrease rate value “IR1”, at block 2220. If the impedance increase ratedoes not exceed the value IR1 (block 2220), operation returns to repeatthe measurement and comparison as described above with reference toblocks 2214 and 2215.

If the impedance increase rate exceeds the value IR1, the impedanceincrease rate is also compared to a second predetermined impedanceincrease rate value “IR2”, at block 2221. If the impedance increase ratedoes not exceed the value IR2 (block 2221), then the power is decreasedby a relatively small amount, at block 2222, and operation returns torepeat the measurement and comparison as described above with referenceto blocks 2214 and 2215.

If the impedance increase exceeds the value IR2 (block 2221), then thedelivered powers is reduced and reapplied at rate R2 to a level L2% thatis less than the previous level, at block 2223; operation then returnsto repeat the impedance measurement and comparison, at blocks 2214 and2215.

With reference to the block numbers of flow chart 2200 as describedabove, example values follow for the variables, but the embodiment isnot limited to these values for the variables: Block VariableApproximate Range 2201 Initial Impedance set point (IL) 5-500 Ω 2202Measured Impedance 100-Infinity Ω 2205 Applied Power 10-150 W 2205Stable Impedance Values 10-250 Ω 2209 Power Ramp (R1) L1/0.5-10 sec 2209Power Level (L1) 50-90% of previous value 2206 Measured Impedance 15-250Ω 2208 Added Power (N1) 1-25 W 2207 Impedance Change 1-20% 2212Frequency of Measured Impedance 0.05-5 sec 2216 Added Power (N2)5-20%/5-60 sec 2217 Cycle Time 1-20 minutes 2218 Impedance (IH)150-Infinite Ω 2220 Impedance Increase Rate (IR1) 0.3-5 W/sec 2221Impedance Increase Rate (IR2) 1-20 W/sec 2223 Power Level % of PreviousValue 65-95 (L2)

While the control algorithm 2200 is described above as being anautomatic process, a manual adaptation of the algorithm 2200 can also beaccomplished. While manual versions of this control process may not beas precise or as repeatable, they are acceptable.

The procedures and algorithms described above for electrode deploymentdepths and corresponding power settings are provided as guides only andmay be modified according to user experience and the thermalrequirements of individual target tissue types. With regard to theInLine™ Radiofrequency Coagulation device described above, thesereference deployment depths and power settings are for reference onlyand are not a substitute for and should not be used in place of theInLine™ Instructions for Use. The user should thoroughly familiarizethemselves with the InLine™ Instructions for Use prior to every use ofthe device, and all Indications, Contraindications, Warnings,Precautions, and Cautions in the InLine™ Instructions for Use should befollowed.

The tissue coagulation system and associated processes described abovecan include other components in a variety of combinations. In additionto the display and controller described above, for example, astereotactic frame or frameless navigator system may be used to directand place the energy director guide/electrodes. Various guide tubes,templates, holding apparatus, arc systems, and spatial digitizers canalso be used to assist in placement of the electrodes in the targettissue. Imaging modalities such as CT, MRI, ultrasound and the like canbe used before, during, or after placement of the electrodes and/orcreation of the coagulation volume.

In addition to including numerous types and combinations of components,there are many alternative embodiments of the tissue coagulation systemcomponents described above. Some of these alternatives includealternative embodiments of the energy director guide and the electrodes,as described below.

The energy director guide of one alternative embodiment includes a softconformal bottom element that forms a conformal surface between thetarget tissue and the energy director guide. The conformal element takeson the shape of the surface of the underlying target tissue. Conformalbottom elements can be constructed from a variety of materials includingsilicone, biocompatible foam rubbers, and urethanes. Conformal bottomelements can also be formed with the use of inflated members.

The energy director guide of various alternative embodiments may take ona variety of shapes including, but not limited to, semi-circular, arcs,and angles. Many other shapes will be recognized by those skilled in theart.

FIG. 23 shows a flexible or semi-flexible guide 2302, under anembodiment. This flexible guide 2302 provides flexibility in two planes.FIG. 24 shows a flexible or semi-flexible guide 2402, under anotheralternative embodiment, that provides flexibility in one plane. Theseguides 2302 and 2402, while being configured to secure and couple powerto the electrodes as described above with reference to FIGS. 2, 3, 8, 9,and 10, permit the user to alter the guide within limits to create adesired shape which, in turn, allows the resulting coagulation plane tomatch the desired outcome or avoid critical anatomical structures. Notethat desired shapes including curved portions are formed from a seriesof coagulation planes having various dimensions, but the embodiment isnot so limited.

These guides 2302 and 2402 can be flexible or semi-flexible in a singleor multiple planes. In a single plane, the guides 2302 and 2402 can beshaped to the tissue targeted below the guide. With a second plane offlexibility, the guides 2302 and 2402 can be used to contour to theshape of the surface or as necessary for location of the operative site.

FIG. 25 is an energy director array including a joining member 2502 thatprovides for simultaneous insertion or retraction of energy directors2504 into target tissue, under an embodiment. The energy directors areconnected to the joining member 2502 to allow for the simultaneousinsertion or retraction of all energy directors 2504 via the energydirector guide 102. As one example, all energy directors 2504 can be ofthe same length, thereby allowing the simultaneous insertion of allenergy directors 2504 to a desired depth within the tissue. This is ofbenefit when a full thickness coagulation plane is desired, there are noanatomical structures that would be contraindicated for the energydirectors, and ease of use is important.

FIG. 26 is an energy director array including a joining member 2602connected to energy directors 2604, under an alternative embodiment.Select energy directors 2604 have non-uniform lengths as they aretailored to match the thickness and shape of the target tissue or organand/or to avoid critical anatomical structures. The joining member 2602,therefore, supports the simultaneous insertion and withdrawal of allenergy directors regardless of length while also supporting theavoidance of critical anatomical structures by the energy directors2604.

The energy directors of an embodiment can be used with a variety ofhousings that enclose the energy directors prior to deployment intotarget tissue. Use of the housing minimizes unintentional deployment ofthe energy directors and reduces the potential for injury of a user orpatient by the energy directors.

Many different types of energy directors can be used with the tissuecoagulation system of an embodiment. Descriptions follow of some exampleenergy directors, but the embodiment is not so limited.

FIG. 27 shows energy directors 2702, 2704, and 2706 supporting deliveryof various agents into the target tissue, under an embodiment. One typeof energy director 2702 supports delivery of agents through a lumen inthe energy director and apertures 2712 around the outer surface of theenergy director 2702.

Another type of energy director 2704 supports delivery of agents througha lumen in the energy director and at least one aperture 2714 in thedistal end of the energy director 2704. Yet another type of energydirector 2706 supports delivery of agents through a lumen in the energydirector in communication with a porous material 2716 around the outersurface of the energy director 2706.

The energy directors 2702, 2704, and 2706 support deliver of agentsincluding, but not limited to, contrast agents used to better visualizesthe detailed anatomy, sclerotic agents to help decrease the overallcirculation in the target region, and chemotherapy agents for use as anadjunctive therapy. Still another example agent is a hyper-tonic orhypo-tonic solution used to create a wet electrode.

FIG. 28 shows energy directors 2804 that capacitively couple to targettissue, under an embodiment. In this embodiment the energy directors2804 are fully, or near-fully insulated. An example of thisconfiguration includes one or more conducting cores 2806 suitable forconducting energy, where the conducting core 2806 is fully or near fullyinsulated with an appropriate dielectric material 2808, coating, orsleeve. The thickness of coating 2808 varies according to the dielectricproperties of the material used as the electrical insulator. Coatingthicknesses of the various embodiments range from approximately 0.00005inch to 0.001 inch, but are not so limited. In this configuration, theenergy directors 2804 induce an energy flow into the target tissue. Whenappropriately applied, this energy would then cause the target tissue toheat and coagulate, as described above. The use of capacitive couplingin this form can increase the relatively low electrical impedance thatresults when several energy directors 2804 are used at a relativelyclose spacing.

The tissue coagulation system of an embodiment includes one or moreenergy directors that support temperature monitoring within and/oraround the target tissue. The temperature monitoring supported by theenergy directors supports the real-time evaluation of a coagulationprocedure both outside and within the effected tissue zone. An exampleof this could be one or more thermocouples arranged in a configurationsuitable for placement within the tissue, for example on and/or withinan associated energy director, wherein the thermocouples couple totemperature monitoring equipment known in the art.

In generating coagulative ablation, the tissue coagulation system andassociated procedures of an embodiment deliver energy that results intissue core temperatures approximately in the range between 65 degreesCelsius and 80 degrees Celsius in the coldest portions of the targettissue volume. The coldest portions of the target tissue volume aretypically those areas that are the most distant from the energydirectors or are thermally shielded from the effect of the energydirectors by other anatomical structures.

Likewise, the tissue coagulation system and associated proceduresdeliver energy that results in tissue core temperatures approximately inthe range between 85 degrees Celsius and 105 degrees Celsius in thewarmest portions of the target tissue volume. At temperatures belowthis, procedural times may be unnecessarily extended. At temperaturesabove this, instability may result due to the superficial charringcaused by the excessive tissue heating. As noted herein, theseconditions can be further mitigated with the use of other factors suchhas hypertonic agents. In particular, a continuous infusion of a 0.9% to8% saline solution at an approximate rate of between 0.01 cc/min to 0.5cc/min will aid in preventing tissue charring.

The temperature monitoring energy director provides the ability tocontrol the energy delivered to the target tissue by controlling theenergy with the use of a closed- or open-loop temperature feedbacksystem. As such, optimum energy delivery can be achieved, therebyavoiding over delivery or under delivery of energy. Over delivery ofenergy can create superficially charred tissue resulting in a reductionor inability to deliver energy and an incomplete coagulation. Underdelivery of energy could significantly increase the procedural durationor even prevent the ability to complete the procedure. By controllingthe transfer of energy to the target tissue in this manner, and by usingnon-stick surfaces such as fluoropolymers like polypropelene andparylene on the energy directors, charring can be minimized to produceoptimal energy delivery and tissue coagulation. In addition, the use oftemperature monitoring also provides evidence and feedback as to thecompletion of the procedure, as described above.

As described above, the energy director guide of an embodimentconfigures the energy directors to provide approximately uniform poweror energy distribution through the target tissue volume. Alternativeembodiments of the tissue coagulation system support the application ofnon-uniform energy distribution via either linear or non-linearly spacedarrays. This configuration monitors a parameter such as temperature,power, or impedance and, in response, controls the delivered energy tomaintain the parameter(s) within a desired target range. By usingindividual energy channels for each bipolar pair, the energy can easilybe altered as needed. For example, with a temperature goal of 80 degreesCelsius after initial ramps of 1.5 minutes to full power, or apredetermined maximum power, the time-temperature slopes are evaluatedfor each zone based on a predetermined ramp (approximately in the rangeof 50-80 degrees Celsius/minute). Based on the temperature ramp thepower is altered to better match the desired rate.

Note that patient and procedure selection is the responsibility of themedical professional-user and the outcome is dependent on manyvariables, including patient anatomy, pathology, and surgicaltechniques. Use of the tissue coagulation system and methods describedherein for thermal coagulation necrosis of soft tissues as an aid duringtissue resection can result in localized elevated temperatures that cancause thermal injury to the skin. In addition, tissue or organs adjacentto the tissue being ablated may be injured thermally. To minimize thepotential for thermal injury to the skin or adjacent tissues,temperature-modifying measures can be initiated at the physician'sdiscretion. These may include separation/isolation of tissue beingtreated from adjacent tissue and/or structures and in addition applyinga sterile ice pack or saline-moistened gauze to cool and/or separatetissues, but are not so limited.

Bloodless or near bloodless transaction of solid organs has beendemonstrated with the ILRFA device described herein during studies ofthe effect of blood loss during transection of livers, kidneys andspleens in sheep. This study was undertaken after the experimentalprotocol was approved by the Animal Ethics Committee of The Universityof New South Wales (study number A02/95).

The ILRFA device used in the study was six (6) centimeters long andincluded six (6) variably deployable electrodes. The ILRFA device usedbipolar radiofrequency energy to form a plane of coagulated tissue forbloodless transaction of solid organs. Power for the ILRFA device wasgenerated using a 1500 RITA generator (Rita Medical Systems, Sunnyvale,Calif.) which had a maximum power of 150 Watts. The generator wasconnected to a laptop computer and the data displayed and recordedgraphically. The amount of power applied was based on the depth ofresection from studies on bench liver.

For the study, all sheep were induced using Zoletil 100 (Virbac NSW,Australia). Sheep were intubated and general anaesthesia was maintainedusing Halothane (1-2%). The sheep's pulse and blood oxygen saturationwas monitored continuously and the blood pressure was recorded everyfifteen minutes. This was undertaken to ensure maintenance of normalvital signs which otherwise could have affected bleeding volume andrate.

After use of ILRFA on the spleen, kidney, and liver in sheep, organtransection was performed with diathermy. The area was then matched witha corresponding resection on the same organ without the benefit of theILRFA device. The amount of bleeding was measured by weighing swabs.

These studies included the performance of a total of eight splenic, fivehepatic, and five kidney resections in sheep that compared the use ofILRFA and diathermy resection with diathermy resection alone. Theresults for the liver resections were as follows: mean blood loss usingILRFA was 43.2+/−36 milliliters (mls); mean blood loss without use ofILRFA was 221.8+/−147 mls; P value 0.005. The results for the kidneyresections were as follows: mean blood loss using ILRFA was 86.4+/−106mls; mean blood loss without use of ILRFA was 388.2+/−152 mls; P value0.02. The results for the spleen resections were as follows: mean bloodloss using ILRFA was 33.1+/−17 mls; mean blood loss without use of ILRFAwas 123.4+/−72 mls; P value 0.005.

Subsequent to the studies of the effect of blood loss during transectionof livers, kidneys and spleens in sheep described above, a study wasperformed on human beings. Eight patients were used in the study, andall operations were performed under general anaesthesia after themobilization of the liver and intraoperative ultrasound. No attempt wasmade to produce a low central venous pressure (“CVP”) and no Pringleinflow occlusion maneuver was performed. At surgery, the plane ofresection was marked with diathermy. One limb of the resection plane wasthen ablated with ILRFA and resected using the ultrasonic aspirator(Selector, Integra Neurosciences, UK). The remaining portion of theliver resection plane was resected with the ultrasonic aspirator ascontrol for ILRFA.

The ILRFA device used in the study was a device five (5) centimeterslong that included six (6) electrodes spaced along the device, each ten(10) centimeters long. Each electrode can be deployed to variable depthsin the hepatic parenchyma. The ILRFA device was connected to a RITA 1500generator. Power was applied to the ILRFA device based on the depth ofelectrode deployment as follows: 25 Watts applied when electrodedeployment depth is one (1) centimeter; 35 Watts applied when electrodedeployment depth is two (2) centimeters; 45 Watts applied when electrodedeployment depth is three (3) centimeters; 55 Watts applied whenelectrode deployment depth is four (4) centimeters; and 60 Watts appliedwhen electrode deployment depth is five (5) centimeters.

All operations proceeded as planned, and there was no morbidity ormortality. The post-operative stay was 9 to 12 days. The mean volume ofbleeding per square centimeter using ILRFA was 6.5+/−3.7 mls, while themean volume of bleeding per square centimeter using the ultrasonicaspirator alone was 20.4+/−8.7 mls. Therefore the ILRFA significantlyreduced bleeding per square centimeter (p=0.004). All of the non-ILRFAresected surfaces required the use of Argon beam coagulation, while nosurfaces treated with the ILRFA device required Argon beam coagulation.

The medical systems described above include a system including an energysource. The system of an embodiment includes an electrode arraycomprising bipolar electrodes positioned so a first spacing between apair of adjacent electrodes is different relative to a second spacingbetween at least one other pair of adjacent electrodes. The electrodearray and the energy source of an embodiment are coupled and configuredto generate uniform energy density in target tissue in response toimpedance of the target tissue.

The first spacing of an embodiment includes a first spacing amongcentral electrodes of the electrode array that is relatively larger thana second spacing between at least one pair of peripheral electrodes ofthe electrode array.

The impedance of the target tissue is determined in an embodiment usinga plurality of impedance measurements and controlled through comparisonto at least one pre-specified impedance threshold.

The energy source of an embodiment generates a wave form that iscritically damped. At least one damping parameter of the wave form isdetermined using at least one property of the target tissue.

The energy source of an embodiment generates a modulated wave form. Atleast one modulation parameter of the modulated wave form is determinedusing at least one property of the target tissue.

At least one electrode of the electrode array of an embodiment isconfigured as a sensor, and the impedance is determined using a changein at least one property of the target tissue as determined frominformation of the sensor.

The electrode array of an embodiment generates controlled hemostasis inthe target tissue.

The generating of uniform energy density in target tissue of anembodiment includes controlling the energy delivery in accordance withimpedance. Controlling energy delivery of an embodiment comprisessetting an initial impedance level according to a type of the targettissue, measuring a first impedance of the target tissue, and initiatingthe energy delivery to the target tissue when the first impedance isgreater than the initial impedance level, wherein initiating the energydelivery includes energy delivery at a first level that is determinedaccording to the initial impedance level.

Controlling energy delivery of an embodiment comprises measuring asecond impedance of the target tissue, and comparing the secondimpedance to the first impedance.

Controlling energy delivery of an embodiment comprises increasing theenergy delivery to a second level when the comparing indicates arelatively steady impedance of the target tissue.

Controlling energy delivery of an embodiment comprises reducing theenergy delivery to a third level when the comparing indicates arelatively increasing impedance of the target tissue.

Controlling energy delivery of an embodiment comprises increasing theenergy delivery at a first rate to a fourth level.

Controlling energy delivery of an embodiment comprises maintaining theenergy delivery at a present level when the comparing indicates arelatively decreasing impedance of the target tissue.

Controlling energy delivery of an embodiment comprises measuring a thirdimpedance of the target tissue, and comparing the third impedance to atleast one previously measured impedance.

Controlling energy delivery of an embodiment comprises maintaining theenergy delivery at a present level when the comparing indicates arelatively decreasing impedance of the target tissue.

Controlling energy delivery of an embodiment comprises increasing theenergy delivery to a fifth level when the comparing indicates arelatively steady impedance of the target tissue.

Controlling energy delivery of an embodiment comprises determining astate of cycle completion when the comparing indicates a relativelyincreasing impedance of the target tissue.

Controlling energy delivery of an embodiment comprises terminatingenergy delivery to the target tissue when the state of cycle completionis complete and the third impedance exceeds a final impedance level.

Controlling energy delivery of an embodiment comprises measuring afourth impedance of the target tissue, and comparing the fourthimpedance to one or more of a previously measured impedance andincreasing the energy delivery to a sixth level when the state of cyclecompletion is complete and the fourth impedance is relatively steady.

Controlling energy delivery of an embodiment comprises determining arate at which the relatively increasing impedance is increasing, andcomparing the rate to a first increase rate.

The controlling energy delivery of an embodiment comprises, when therate is less than the first increase rate, measuring a fifth impedanceof the target tissue, and comparing the fifth impedance to one or moreof a previously measured impedance and increasing the energy delivery toa seventh level when the state of cycle completion is complete and thefifth impedance is relatively steady.

Controlling energy delivery of an embodiment comprises comparing therate to a second increase rate when the rate is greater than the firstincrease rate.

Controlling energy delivery of an embodiment comprises reducing theenergy delivery to an eighth level when the rate is greater than thesecond increase rate.

Controlling energy delivery of an embodiment comprises increasing theenergy delivery at a second rate to a ninth level.

Controlling energy delivery of an embodiment comprises reducing theenergy delivery to a tenth level when the rate is less than the secondincrease rate.

The medical systems described above include a system including an energysource. The system of an embodiment includes an electrode arraycomprising bipolar electrodes positioned so a first spacing between afirst pair of electrodes is different relative to a second spacingbetween a second pair of electrodes. The electrode array and the energysource are coupled and configured to generate uniform energy density intarget tissue in response to impedance of the target tissue.

The first spacing of an embodiment includes a first spacing amongcentral electrodes of the electrode array that is relatively larger thanthe second spacing between at least one pair of peripheral electrodes ofthe electrode array.

Generating uniform energy density in target tissue of an embodimentincludes controlling the energy delivery in accordance with impedance.Controlling energy delivery of an embodiment comprises setting aninitial impedance level according to a type of the target tissue,measuring an impedance of the target tissue, and initiating the energydelivery to the target tissue, wherein initiating the energy deliveryincludes energy delivery at a first level that is determined accordingto the initial impedance level.

Controlling energy delivery of an embodiment further comprisesincreasing the energy delivery to a second level when the impedance isrelatively steady, and reducing the energy delivery to a third level andthen increasing the energy delivery at a first rate to a fourth levelwhen the impedance is relatively increasing.

Controlling energy delivery of an embodiment comprises maintaining theenergy delivery at a present level when the impedance is relativelydecreasing.

Controlling energy delivery of an embodiment comprises furtherincreasing the energy delivery to a fifth level when the impedance isrelatively steady.

Controlling energy delivery of an embodiment comprises determining astate of cycle completion when the impedance is relatively increasing.

Controlling energy delivery of an embodiment comprises terminatingenergy delivery to the target tissue when the state of cycle completionis complete and the impedance exceeds a final impedance level, andfurther increasing the energy delivery to a sixth level when the stateof cycle completion is complete and the impedance is relatively steady.

Controlling energy delivery of an embodiment comprises furtherincreasing the energy delivery to a seventh level when the state ofcycle completion is complete, a rate at which the impedance isincreasing is less than a first increase rate, and the impedance remainsrelatively steady.

Controlling energy delivery of an embodiment comprises reducing theenergy delivery to an eighth level when the rate at which the impedanceis increasing is greater than a second increase rate, and then furtherincreasing the energy delivery at a second rate to a ninth level.

The medical systems described above include a method for controllinghemostasis in target tissue. The method of an embodiment includesconfiguring an array of bipolar electrodes in the target tissue so afirst spacing between a pair of adjacent electrodes is differentrelative to a second spacing between at least one other pair of adjacentelectrodes. The method of an embodiment includes delivering energy tothe target tissue via the array. The method of an embodiment includescontrolling the delivering according to impedance of the target tissueto generate uniform energy density in the target tissue.

Configuring of an embodiment includes positioning each electrode of theelectrode array at a selected depth in the target tissue.

The method of an embodiment further comprises generating at least oneplane of coagulated tissue in the target tissue.

The first spacing of an embodiment includes a first spacing amongcentral electrodes of the electrode array that is relatively larger thana second spacing between at least one pair of peripheral electrodes ofthe electrode array.

The delivering of an embodiment includes generating a wave form that iscritically damped, wherein at least one damping parameter of the waveform is determined using at least one property of the target tissue.

The delivering of an embodiment includes generating a modulated waveform, wherein at least one modulation parameter of the modulated waveform is determined using at least one property of the target tissue.

Controlling the delivering of an embodiment includes controlling thedelivering in accordance with impedance. Controlling of an embodimentcomprises setting an initial impedance level according to a type of thetarget tissue, measuring a first impedance of the target tissue, andinitiating the energy delivery to the target tissue when the firstimpedance is greater than the initial impedance level, whereininitiating the energy delivery includes energy delivery at a first levelthat is determined according to the initial impedance level.

Controlling of the method of an embodiment includes measuring a secondimpedance of the target tissue, and comparing the second impedance tothe first impedance.

Controlling of the method of an embodiment includes increasing energydelivery to a second level when the comparing indicates a relativelysteady impedance of the target tissue.

Controlling of the method of an embodiment includes reducing energydelivery to a third level when the comparing indicates a relativelyincreasing impedance of the target tissue.

Controlling of the method of an embodiment includes increasing energydelivery at a first rate to a fourth level.

Controlling of the method of an embodiment includes maintaining energydelivery at a present level when the comparing indicates a relativelydecreasing impedance of the target tissue.

Controlling of the method of an embodiment includes measuring a thirdimpedance of the target tissue, and comparing the third impedance to atleast one previously measured impedance.

Controlling of the method of an embodiment includes maintaining energydelivery at a present level when the comparing indicates a relativelydecreasing impedance of the target tissue.

Controlling of the method of an embodiment includes increasing energydelivery to a fifth level when the comparing indicates a relativelysteady impedance of the target tissue.

Controlling of the method of an embodiment includes determining a stateof cycle completion when the comparing indicates a relatively increasingimpedance of the target tissue.

Controlling of the method of an embodiment includes terminating energydelivery to the target tissue when the state of cycle completion iscomplete and the third impedance exceeds a final impedance level.

Controlling of the method of an embodiment includes measuring a fourthimpedance of the target tissue, and comparing the fourth impedance toone or more of a previously measured impedance and increasing energydelivery to a sixth level when the state of cycle completion is completeand the fourth impedance is relatively steady.

Controlling of the method of an embodiment includes determining a rateat which the relatively increasing impedance is increasing, andcomparing the rate to a first increase rate.

Controlling of the method of an embodiment includes, when the rate isless than the first increase rate measuring a fifth impedance of thetarget tissue, and comparing the fifth impedance to one or more of apreviously measured impedance and increasing energy delivery to aseventh level when the state of cycle completion is complete and thefifth impedance is relatively steady.

Controlling of the method of an embodiment includes comparing the rateto a second increase rate when the rate is greater than the firstincrease rate.

Controlling of the method of an embodiment includes reducing energydelivery to an eighth level when the rate is greater than the secondincrease rate.

Controlling of the method of an embodiment includes increasing energydelivery at a second rate to a ninth level.

Controlling of the method of an embodiment includes reducing energydelivery to a tenth level when the rate is less than the second increaserate.

A tissue coagulation system described above comprises: an energy source;two or more pairs of bipolar energy directors configured for insertioninto a volume of biological tissue; and an energy director guide thatconfigures the energy directors to generate at least one plane ofcoagulated tissue in the volume of tissue by coupling energy from theenergy source to the volume of tissue, wherein the energy directorconfiguration results in approximately uniform energy distributionthrough the tissue volume; wherein the guide includes a series ofchannels that receive the energy directors in an alternating polarityseries, wherein spacing among the channels varies according to a numberof pairs of energy directors received in the energy director guide sothat relative spacing among the center-most channels is largest andrelative spacing among the end-most channels is smallest; and whereinthe guide independently couples the energy source to each of the energydirectors.

The tissue coagulation system of an embodiment comprises an energysource that includes a radio frequency generator.

The energy director guide of an embodiment further secures a selecteddepth position of the energy directors in the tissue volume.

The two or more pairs of bipolar energy directors of an embodimentinclude three pairs of bipolar energy directors. Alternatively, the twoor more pairs of bipolar energy directors of an embodiment include fourpairs of bipolar energy directors.

The energy directors of an embodiment further include at least onecomponent selected from among temperature sensors, thermocouples,infusion components, and optical tissue monitors.

The tissue coagulation system of an embodiment further comprises atleast one controller coupled among the energy source and the bipolarenergy directors, wherein the controller supports automatic control ofenergy delivery to each of the bipolar energy directors.

The energy directors of an embodiment are inserted to independentlyvariable depths in the volume of biological tissue.

The energy directors of an embodiment are internally cooled.

The tissue coagulation system of an embodiment further comprises atleast one housing, wherein the housing includes the energy directors andis configured to couple to the energy director guide, wherein the energydirectors are deployed from the housing and inserted into the volume ofbiological tissue.

The uniform energy distribution of an embodiment includes uniformcurrent density.

The alternating polarity series of an embodiment includes at least oneelectrode of a positive polarity in series with at least one electrodeof a negative polarity.

A system described above for generating at least one plane of coagulatedtissue in a volume of biological tissue comprises at least one guideincluding a series of channels that configure two or more sets ofbipolar electrodes in an alternating polarity series, wherein spacingamong the channels varies according to a total number of bipolarelectrodes received in the guide so that relative spacing among thecenter-most channels is largest and relative spacing among the end-mostchannels is smallest, wherein the guide secures a selected position ofeach of the electrodes in the target biological tissue and couples eachbipolar electrode to at least one energy source.

A method for use with the tissue coagulation systems described above forgenerating at least one plane of coagulated tissue in biological tissue,comprises: positioning an electrode guide on a surface of a biologicaltissue region that includes a target tissue volume, wherein theelectrode guide includes a series of channels that configure two or morepairs of bipolar electrodes in an alternating polarity series, whereinspacing among the channels varies according to a total number of bipolarelectrodes received in the guide so that relative spacing among thecenter-most channels is largest and relative spacing among the end-mostchannels is smallest; securing the bipolar electrodes at a selecteddepth in the target tissue volume using the electrode guide; coupling atleast one energy source to the bipolar electrodes using the electrodeguide and providing approximately uniform energy distribution throughthe target tissue volume; and generating the at least one plane ofcoagulated tissue in the target tissue volume. The method for use withtissue coagulation systems of an embodiment further comprises infusing asolution into the target tissue volume via at least one of the bipolarelectrodes, wherein the solution is at least one of a hyper-tonicsolution, a hypo-tonic solution, a contrast agent, a sclerotic agent,and a chemotherapy agent.

A method for use with the tissue coagulation systems described above forgenerating a plane of coagulated tissue in biological tissue, comprises:positioning an electrode guide in proximity to a target tissue volume;inserting two or more pairs of bipolar electrodes into the target tissuevolume in a series of alternating polarity via the electrode guide;securing the bipolar electrodes at a selected depth in the target tissuevolume using components of the electrode guide; coupling at least oneenergy source to the target tissue volume via the bipolar electrodes;controlling energy delivery to effect approximately uniform energydistribution through the target tissue volume, wherein a targettemperature in the target tissue volume is greater than a temperatureapproximately in the range of 55 degrees Celsius to 60 degrees Celsius;and generating the plane of coagulated tissue in the target tissuevolume. The method further comprises measuring the target temperature atone or more of the electrodes. The method further comprises measuringthe target temperature at one or more points in the target tissuevolume.

A tissue coagulation apparatus described above for use in a resectionprocedure of tissue within a mammalian body, comprises: a support bodyhaving a first and second end portions and a surface extending betweenthe first and second end portions; and a plurality of at least first,second and third elongate radio frequency electrodes carried by thesupport body and extending from the surface in spaced-apart positionsbetween the first and second end portions, the first and secondelectrodes being spaced apart by a first distance and the second andthird electrodes being spaced apart by a second distance different thanthe first distance, the first and second distances being chosen so thatwhen the first, second and third electrodes are disposed in the tissuethe energy distribution between the first and second electrodes and theenergy distribution between the second and third electrodes areapproximately uniform.

The first, second and third electrodes of an embodiment are parallel.

The first, second and third electrodes of an embodiment are needleelectrodes.

The tissue coagulation apparatus described above for use in a resectionprocedure of tissue within a mammalian body further comprises a fourthelongate radio frequency electrode spaced from the third electrode by athird distance different from the first and second distances, the thirddistance being chosen so that when the second, third and fourthelectrodes are disposed in the tissue the energy distribution betweenthe second and third electrodes and the energy distribution between thethird and fourth electrodes are approximately uniform.

The tissue coagulation apparatus of an embodiment described above foruse in a resection procedure of tissue within a mammalian body furthercomprises a radio frequency generator coupled to the first and secondelectrodes for supplying a first potential to the first electrode and asecond potential to the second electrode.

The tissue coagulation apparatus of an embodiment described above foruse in a resection procedure of tissue within a mammalian body furthercomprises a radio frequency generator coupled to the radio frequencyelectrodes for supplying a first potential to the first and secondelectrodes and a second potential to the third and fourth electrodes.

A method for use with the tissue coagulation systems described above forresecting a portion of a target organ within a mammalian body using asupport body having a first and second end portions and a surfaceextending between the first and second end portions and a plurality ofelectrodes extending from the surface and spaced sequentially betweenthe first and second end portions, comprises: positioning the electrodesin the vicinity of the target organ; extending the electrodes into thetarget organ; supplying a first potential of radio frequency energy to afirst group of the plurality of electrodes and a second potential ofradio frequency energy to a second group of the plurality of electrodesso that radio frequency energy travels between the first and secondgroups of electrodes and thus forms a wall of ablated tissue in thetarget organ; and incising the target organ in the vicinity of the wallof ablated tissue to resect the portion of the target organ.

The method for resecting a portion of a target organ further comprisesestimating a transverse dimension of the target organ and sizing theelectrodes as a function of the transverse dimension to prevent theelectrodes from extending beyond the target organ when the surface issubstantially flush with the target organ.

The method for resecting a portion of a target organ further comprisesseparating the target organ from an adjacent organ to prevent theelectrodes from piercing the adjacent organ when the electrodes areextended into the target organ. The separation of an embodiment isachieved by placing a shield between the target organ and the adjacentorgan to protect the adjacent organ from the electrodes.

A coagulation system described above for use in biological tissue,comprises a handle, a radiofrequency (RF) generator, and an electrodearray including two or more pair of bipolar electrodes slideably coupledin channels of the handle and electrically coupled to the RF generator,the electrode array configured to deliver a balanced energy density in atarget volume of the biological tissue, wherein the balanced energydensity results in thermal coagulation necrosis of a rectangular volumeof biological tissue.

The rectangular volume of tissue of an embodiment has a widthapproximately in a range of 0.5 centimeter to 1 centimeter.

The electrodes of the electrode array of an embodiment are each insertedto independently variable depths in the target volume of biologicaltissue and the handle secures a selected depth position.

The two or more pairs of bipolar electrodes of an embodiment include atleast one of three pairs of bipolar electrodes and four pairs of bipolarelectrodes.

The system of an embodiment further comprises at least one temperaturesensor. The temperature sensor of an embodiment is a component of one ormore of the bipolar electrodes, but is not so limited.

The system of an embodiment further comprises at least one thermocouple.

The system of an embodiment further comprises a controller coupled amongthe RF generator and the bipolar electrodes to provide automatic controlof energy delivery to each of the bipolar electrodes.

One of more of the bipolar electrodes of an embodiment includes at leastone internal passage configured to carry fluid.

The bipolar electrodes of the electrode array of an embodiment arearranged in an alternating polarity series that includes at least onebipolar electrode of a positive polarity in series with at least onebipolar electrode of a negative polarity.

Configuring the electrode array of an embodiment to deliver a balancedenergy density includes positioning the bipolar electrodes in the arrayaccording to at least one of a total number of bipolar electrodes in theelectrode array, a diameter of each bipolar electrode, and a selecteddeployment depth of each bipolar electrode.

A coagulation system of an embodiment comprises a radiofrequency (RF)generator and an electrode array including two or more pair of bipolarelectrodes slideably coupled in channels of a handle and electricallycoupled to the RF generator. The electrode array is configured todeliver a balanced energy density in a target volume of the biologicaltissue using at least one of irregular spacing between the channels andelectrodes having one or more different diameters, wherein the balancedenergy density results in thermal coagulation necrosis of a rectangularvolume of biological tissue.

Spacing among the bipolar electrodes of an embodiment decreases towardsone or more ends of the electrode array.

Spacing among the bipolar electrodes of an embodiment varies accordingto at least one of a total number of bipolar electrodes in the electrodearray, the electrode diameters, and the selected deployment depth ofeach electrode.

The balanced energy density of an embodiment includes uniform energydistribution and uniform current density.

The system of an embodiment further comprises at least one sensor.

The rectangular volume of tissue of an embodiment has a widthapproximately in a range of 0.5 centimeter to 1 centimeter.

A tissue coagulation system of an embodiment comprises a radiofrequency(RF) generator and an electrode array including two or more pair ofbipolar electrodes slideably coupled in channels of a hand-piece andelectrically coupled to the RF generator. The electrode array and RFgenerator are configured to deliver uniform energy density in a targetvolume of the biological tissue by delivering the energy to targettissue and controlling the delivery in response to at least one ofelapsed time of the delivery, a temperature of the target tissue volume,and an impedance of the target tissue volume, wherein the balancedenergy density results in thermal coagulation necrosis of a rectangularvolume of biological tissue. The rectangular volume of tissue of anembodiment has a width approximately in a range of 0.5 centimeter to 1centimeter.

The temperature of the target tissue volume includes at least one of atemperature of at least one area of the target tissue volume, a changein temperature of at least one area of the target tissue volume, and arate of change of temperature of at least one area of the target tissuevolume.

The system of an embodiment further comprises at least one sensor forsensing at least one of the temperature and the impedance of the targettissue volume.

In the system of an embodiment, controlling the delivery in response toat least one of elapsed time of the delivery, a temperature of thetarget tissue volume, and an impedance of the target tissue volumefurther comprises: increasing a delivery rate of energy to the targettissue volume by a first amount; increasing the delivery rate of energywhen a rate of increase of the temperature of the target tissue volumeis equal to or less than a minimum rate; decreasing the delivery rate ofenergy when the rate of increase of the temperature of the target tissuevolume is equal to or greater than a maximum rate; decreasing thedelivery rate of energy when the temperature of the target tissue volumeis greater than a maximum temperature; increasing the delivery rate ofenergy to the target tissue volume by a second amount when thetemperature of the target tissue volume is less than the maximumtemperature; and terminating the delivery of energy to the target tissuevolume when the elapsed time of the delivery exceeds a maximum time.

In the system of an embodiment, controlling the delivery further inresponse to at least one of elapsed time of the delivery, a temperatureof the target tissue volume, and an impedance of the target tissuevolume comprises: increasing a delivery rate of energy to the targettissue volume by a first amount; maintaining the delivery rate of energywhen the impedance of the target tissue is decreasing; and terminatingthe delivery of energy to the target tissue volume when the impedance ofthe target tissue exceeds a maximum impedance. The delivery rate ofenergy to the target tissue volume is further increased by the firstamount when the impedance of the target tissue is increasing orremaining approximately constant.

In the system of an embodiment, controlling the delivery in response toat least one of elapsed time of the delivery, a temperature of thetarget tissue volume, and an impedance of the target tissue volumefurther comprises: determining a first impedance of the target tissuevolume; delivering energy at a first rate to the target tissue volume;monitoring the first impedance and delivering energy at a second ratewhen a decrease in the first impedance is less than a first threshold;determining a second impedance of the target tissue volume in responseto the decrease in the first impedance exceeding the first threshold;monitoring the second impedance and delivering energy at a third ratewhen a decrease in the second impedance is less than a second threshold;and terminating the delivery of energy to the target tissue volume whenthe impedance of the target tissue exceeds a maximum impedance.

In the system of an embodiment, controlling the delivery in response toat least one of elapsed time of the delivery, a temperature of thetarget tissue volume, and an impedance of the target tissue volumefurther comprises: determining the impedance of the target tissuevolume; delivering the balanced energy to the target tissue volume at afirst rate until the impedance stabilizes at a lower impedance; anddelivering the balanced energy to the target tissue volume at a secondrate until the impedance exceeds a threshold impedance.

The tissue coagulation system of an embodiment includes a method forapplying energy to biological tissue in order to provide controlledhemostasis. The method comprises configuring an electrode array thatprovides a uniform energy density in at least one target tissue volumeusing two or more pair of electrodes that include irregular spacingbetween one or more pairs of the electrodes. The method also comprisespositioning each electrode of the electrode array at a selected depth inthe target tissue volume using the configuration. The method alsocomprises generating planes of coagulated tissue in the target tissuevolume by energy delivered to the target tissue volume from at least oneenergy source via the electrodes and controlling the energy delivery inresponse to at least one of elapsed time, a temperature of the targettissue volume, and an impedance of the target tissue volume.

The irregular spacing of an embodiment includes a first spacing amongcentral electrodes of the electrode array that is relatively larger thana second spacing among peripheral electrodes of the electrode array.

The energy delivered in an embodiment is controlled according to atleast one of a pre-determined property of the target tissue volume and arelationship of the electrode array with the target tissue volume.

The energy delivered in an embodiment is controlled according to theimpedance of the target tissue volume, wherein the impedance of thetarget tissue volume is determined using a plurality of impedancemeasurements and controlled through comparison to at least onepre-specified impedance threshold.

The energy delivered in an embodiment is a wave form that is criticallydamped, wherein at least one damping parameter of the wave form isdetermined using at least one property of the target tissue volume.

The method of an embodiment comprises determining a desired level of thehemostasis using a change in at least one property of the target tissuevolume during the energy delivery. The change of an embodiment includesat least one of a change in impedance of the target tissue volume. Thechange in impedance of an embodiment is determined during one or more ofat least one dwell period and during delivery of the energy.

The energy delivered of an embodiment includes electrical energy. Theelectrical energy of an embodiment includes at least one ofhigh-frequency electrical energy, radio frequency (RF) energy, andmicrowave energy.

Controlling the energy delivery in accordance with temperature of anembodiment comprises one or more of increasing the energy delivered tothe target tissue by a first amount, determining a rate of temperaturechange in the target tissue, and further increasing the energy deliveredover the first amount when the rate of temperature change is determinedto be at least one of less than and equal to a first rate.

Controlling the energy delivery in accordance with temperature of anembodiment comprises decreasing the energy delivered when the rate oftemperature change is determined to be at least one of greater than andequal to a second rate. The method of an embodiment further comprisesone or more of determining a rate of temperature change in the targettissue is within a range bounded by the first rate and the second rate,determining a temperature of the target tissue, and decreasing theenergy delivered when the temperature is determined to be greater than amaximum temperature. The energy delivered to the target tissue of anembodiment is increased when the temperature is determined to be lessthan the maximum temperature. The energy delivered to the target tissueis terminated when an elapsed time of the energy delivered to the targettissue is greater than a maximum time.

Controlling the energy delivery in accordance with impedance comprisesone or more of increasing the energy delivered to the target tissue by afirst amount, determining an elapsed time of the energy delivered to thetarget tissue, and determining an impedance of the target tissue. Theenergy delivered to the target tissue of an embodiment is terminatedwhen the elapsed time is greater than a maximum time and the impedanceis greater than a maximum impedance. The energy delivered of anembodiment is increased over the first amount when the elapsed time isapproximately equal to or less than a maximum time and the impedance isapproximately constant or increasing. The energy delivered of anembodiment is maintained at the first amount when the elapsed time isapproximately equal to or less than a maximum time and the impedance isdecreasing. The energy delivered to the target tissue of an embodimentis terminated when the impedance is greater than a maximum impedance.

Controlling the energy delivery in accordance with impedance comprisesone or more of setting an initial impedance level according to a type ofthe target tissue, increasing the energy delivered to the target tissueby a first amount, and determining an impedance of the target tissue.The energy delivered of an embodiment is increased to a second amountthat is greater than the first amount when the impedance has decreasedto a first decreased impedance that is equal to or greater than a firstthreshold impedance. The energy delivered of an embodiment is maintainedat the first amount when the impedance has decreased to a firstdecreased impedance that is less than a first threshold impedance.

The method of an embodiment includes setting the first decreasedimpedance as a second threshold impedance.

The method of an embodiment maintains the energy delivered at the secondamount when the impedance has decreased to a second decreased impedancethat is less than the second threshold impedance.

The method of an embodiment increases the energy delivered to a thirdamount that is greater than the second amount when the second decreasedimpedance is equal to or greater than the second threshold impedance.

The method of an embodiment determines a total amount of energydelivered to the target tissue since initial application of the energydelivered.

The method of an embodiment increases the energy delivered when thetotal amount of energy delivered is less than a maximum energy.

The method of an embodiment maintains the energy delivered at the thirdamount when the total amount of energy delivered is equal to or greaterthan the maximum energy. The method of an embodiment determines theimpedance of the target tissue. The method of an embodiment determines atotal amount of energy delivered to the target tissue since initialapplication of the energy delivered when the impedance is less than orequal to a third threshold impedance. The method of an embodimentterminates the energy delivered to the target tissue when the impedanceis greater than the third threshold impedance.

The tissue coagulation system of an embodiment includes a system forperforming controlled hemostasis in biological tissue. The system of anembodiment includes at least one generator. The system includes anelectrode array slideably coupled in channels of a hand-piece andelectrically coupled to the generator, the electrode array including twoor more pair of bipolar electrodes that includes irregular spacingbetween one or more pairs of the electrodes, the electrode array andgenerator configured to deliver uniform energy density in a targetvolume of the biological tissue by delivering the energy to targettissue and controlling the delivery in response to at least one ofelapsed time of the delivery, a temperature of the target tissue volume,and an impedance of the target tissue volume.

The irregular spacing of an embodiment includes a first spacing amongcentral electrodes of the electrode array that is relatively larger thana second spacing among peripheral electrodes of the electrode array.

The energy delivered in an embodiment is controlled according to theimpedance of the target tissue volume, wherein the impedance of thetarget tissue volume is determined using a plurality of impedancemeasurements and controlled through comparison to at least onepre-specified impedance threshold.

The energy delivered in an embodiment is a wave form that is criticallydamped, wherein at least one damping parameter of the wave form isdetermined using at least one property of the target tissue volume.

The system of an embodiment includes at least one electrode configuredas at least one sensor, wherein a desired level of the hemostasis isdetermined using a change in at least one property of the target tissuevolume during the energy delivery as determined from information of theat least one sensor.

The system of an embodiment includes a controller that controls theenergy delivered according to at least one of a pre-determined propertyof the target tissue volume and a relationship of the electrode arraywith the target tissue volume.

The control of an embodiment includes controlling the energy delivery inaccordance with temperature, comprising one or more of increasing theenergy delivered to the target tissue by a first amount, determining arate of temperature change in the target tissue, and further increasingthe energy delivered over the first amount when the rate of temperaturechange is determined to be at least one of less than and equal to afirst rate.

The system of an embodiment decreases the energy delivered when the rateof temperature change is determined to be at least one of greater thanand equal to a second rate.

The system of an embodiment determines a rate of temperature change inthe target tissue is within a range bounded by the first rate and thesecond rate, determines a temperature of the target tissue, decreasesthe energy delivered when the temperature is determined to be greaterthan a maximum temperature, increases the energy delivered to the targettissue when the temperature is determined to be less than the maximumtemperature, and/or terminates the energy delivered to the target tissuewhen an elapsed time of the energy delivered to the target tissue isgreater than a maximum time.

The control of an embodiment includes controlling the energy delivery inaccordance with impedance, comprising one or more of increasing theenergy delivered to the target tissue by a first amount, determining anelapsed time of the energy delivered to the target tissue, anddetermining an impedance of the target tissue.

The system of an embodiment further includes one or more of terminatingthe energy delivered to the target tissue when the elapsed time isgreater than a maximum time and the impedance is greater than a maximumimpedance, and further increasing the energy delivered over the firstamount when the elapsed time is approximately equal to or less than amaximum time and the impedance is approximately constant or increasing.

The system of an embodiment further includes one or more of maintainingthe energy delivered at the first amount when the elapsed time isapproximately equal to or less than a maximum time and the impedance isdecreasing, and terminating the energy delivered to the target tissuewhen the impedance is greater than a maximum impedance.

The control of an embodiment includes controlling the energy delivery inaccordance with impedance, comprising one or more of setting an initialimpedance level according to a type of the target tissue, increasing theenergy delivered to the target tissue by a first amount, and determiningan impedance of the target tissue.

The system of an embodiment further includes one or more of increasingthe energy delivered to a second amount that is greater than the firstamount when the impedance has decreased to a first decreased impedancethat is equal to or greater than a first threshold impedance, andmaintaining the energy delivered at the first amount when the impedancehas decreased to a first decreased impedance that is less than a firstthreshold impedance.

The system of an embodiment further includes one or more of setting thefirst decreased impedance as a second threshold impedance, maintainingthe energy delivered at the second amount when the impedance hasdecreased to a second decreased impedance that is less than the secondthreshold impedance, and increasing the energy delivered to a thirdamount that is greater than the second amount when the second decreasedimpedance is equal to or greater than the second threshold impedance.

The system of an embodiment further includes one or more of determininga total amount of energy delivered to the target tissue since initialapplication of the energy delivered, increasing the energy deliveredwhen the total amount of energy delivered is less than a maximum energy,and maintaining the energy delivered at the third amount when the totalamount of energy delivered is equal to or greater than the maximumenergy.

The system of an embodiment further includes one or more of determiningthe impedance of the target tissue, determining a total amount of energydelivered to the target tissue since initial application of the energydelivered when the impedance is less than or equal to a third thresholdimpedance, and terminating the energy delivered to the target tissuewhen the impedance is greater than the third threshold impedance.

Following are one or more examples of additional embodiments of thetissue ablation devices, each of which may be used alone or incombination with other embodiments described herein.

The tissue coagulation systems and methods described above operate inone or more of a mono-polar or bi-polar configuration and switch betweenvarious electrodes thereby creating different groups of activeelectrodes and creating different paths of current flow upon applicationof energy to the target tissue.

The tissue coagulation systems and methods described above operate inone or more of a mono-polar or bi-polar configuration and switch betweenvarious electrodes thereby creating different groups of activeelectrodes and creating different paths of current flow upon applicationof energy to the target tissue, and/or to continue to switch in anycombination and for any number of times.

The tissue coagulation systems and methods described above operate inone or more of a mono-polar or bi-polar configuration and switch betweenvarious electrodes thereby creating different groups of activeelectrodes and creating different paths of current flow upon applicationof energy to the target tissue, and/or to continue to switch in anycombination and for any number of times, and/or the ability to switchwith or without the reduction of applied power-switch on the fly.

The tissue coagulation systems and methods described above operate inone or more of a mono-polar or bi-polar configuration and switch betweenvarious electrodes thereby creating different groups of activeelectrodes and creating different paths of current flow upon applicationof energy to the target tissue, and/or to continue to switch in anycombination and for any number of times, and/or the ability to switchwith or without the reduction of applied power-switch on the fly, and/orto alter the applied energy prior to switching.

The tissue coagulation systems and methods described above operate inone or more of a mono-polar or bi-polar configuration and switch betweenvarious electrodes thereby creating different groups of activeelectrodes and creating different paths of current flow upon applicationof energy to the target tissue, and/or to continue to switch in anycombination and for any number of times, and/or the ability to switchwith or without the reduction of applied power-switch on the fly, and/orto alter the applied energy prior to switching, and/or to switch basedon fixed or changing tissue characteristics including, but not limitedto, tissue temperature, impedance, rate of change of temperature, andrate of change of impedance, for example.

The tissue coagulation systems and methods described above furtherinclude the use of various types, combinations, and/or configurations ofelectrode coatings or other means to locally lower the impedanceof/around the system electrodes without significantly reducing theimpedance a large (several electrode diameters or width) distance awayfrom the electrode; e.g., application of energy in such a way and/or forthe purpose of releasing conductive interstitial cellular fluid or acoating of salt crystals on the electrodes.

The tissue coagulation systems and methods described above allow for theapplication of energy followed by a reduction or dwell time followed bythe application or reapplication of energy to aid in the application ofhigher amounts of energy. This may be performed using various wave formssuch as saw-tooth, square wave, and the like including, but not limitedto, controlling the delivery of energy to a level at or near zero (0).

The tissue coagulation systems and methods described above allow for theapplication of energy followed by a reduction or dwell time followed bythe application or reapplication of energy to aid in the application ofhigher amounts of energy. This may be performed using various wave formssuch as saw-tooth, square wave, and the like including, but not limitedto, controlling the delivery of energy to a level at or near zero (0),and/or the energy delivered is reduced or eliminated with/atapproximately the same time the energy is increased between otherelectrodes/electrode pairs or some of the current and some otherelectrodes within the device.

The tissue coagulation systems and methods described above allow for theapplication of energy followed by a reduction or dwell time followed bythe application or reapplication of energy to aid in the application ofhigher amounts of energy. This may be performed using various wave formssuch as saw-tooth, square wave, and the like including, but not limitedto, controlling the delivery of energy to a level at or near zero (0),and/or the energy delivered is reduced or eliminated with/atapproximately the same time the energy is increased between otherelectrodes/electrode pairs or some of the current and some otherelectrodes within the device, for any combinations, durations, fixed orvarying power levels and for any duration or number of cycles.

The tissue coagulation systems and methods described above allow for theapplication of energy followed by a reduction or dwell time followed bythe application or reapplication of energy to aid in the application ofhigher amounts of energy. This may be performed using various wave formssuch as saw-tooth, square wave, and the like including, but not limitedto, controlling the delivery of energy to a level at or near zero (0).

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in a sense of “including,but not limited to.” Words using the singular or plural number alsoinclude the plural or singular number respectively. Additionally, thewords “herein,” “hereunder,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. When the word “or” is usedin reference to a list of two or more items, that word covers all of thefollowing interpretations of the word: any of the items in the list, allof the items in the list and any combination of the items in the list.

The above description of illustrated embodiments of the tissuecoagulation system is not intended to be exhaustive or to limit thetissue coagulation system to the precise form disclosed. While specificembodiments of, and examples for, the tissue coagulation system aredescribed herein for illustrative purposes, various equivalentmodifications are possible within the scope of the tissue coagulationsystem, as those skilled in the relevant art will recognize. Theteachings of the tissue coagulation system provided herein can beapplied to other coagulation systems, resection systems, and medicaldevices, not only for the tissue coagulation system described above.

The elements and acts of the various embodiments described above can becombined to provide further embodiments. These and other changes can bemade to the tissue coagulation system in light of the above detaileddescription.

1. A system comprising: an energy source; and an electrode arraycomprising bipolar electrodes positioned so a first spacing between apair of adjacent electrodes is different relative to a second spacingbetween at least one other pair of adjacent electrodes, wherein theelectrode array and the energy source are coupled and configured togenerate uniform energy density in target tissue in response toimpedance of the target tissue.
 2. The system of claim 1, wherein thefirst spacing includes a first spacing among central electrodes of theelectrode array that is relatively larger than a second spacing betweenat least one pair of peripheral electrodes of the electrode array. 3.The system of claim 1, wherein the impedance of the target tissue isdetermined using a plurality of impedance measurements and controlledthrough comparison to at least one pre-specified impedance threshold. 4.The system of claim 1, wherein the energy source generates a wave formthat is critically damped, wherein at least one damping parameter of thewave form is determined using at least one property of the targettissue.
 5. The system of claim 1, wherein the energy source generates amodulated wave form, wherein at least one modulation parameter of themodulated wave form is determined using at least one property of thetarget tissue.
 6. The system of claim 1, wherein at least one electrodeof the electrode array is configured as a sensor, wherein the impedanceis determined using a change in at least one property of the targettissue as determined from information of the sensor.
 7. The system ofclaim 1, wherein the electrode array generates controlled hemostasis inthe target tissue.
 8. The system of claim 1, wherein generating uniformenergy density in target tissue in response to impedance includescontrolling the energy delivery in accordance with impedance, whereincontrolling comprises: setting an initial impedance level according to atype of the target tissue; measuring a first impedance of the targettissue; initiating the energy delivery to the target tissue when thefirst impedance is greater than the initial impedance level, whereininitiating the energy delivery includes energy delivery at a first levelthat is determined according to the initial impedance level.
 9. Thesystem of claim 8, wherein controlling comprises: measuring a secondimpedance of the target tissue; comparing the second impedance to thefirst impedance.
 10. The system of claim 9, wherein controllingcomprises increasing the energy delivery to a second level when thecomparing indicates a relatively steady impedance of the target tissue.11. The system of claim 9, wherein controlling comprises reducing theenergy delivery to a third level when the comparing indicates arelatively increasing impedance of the target tissue.
 12. The system ofclaim 11, wherein controlling comprises increasing the energy deliveryat a first rate to a fourth level.
 13. The system of claim 11, whereincontrolling comprises maintaining the energy delivery at a present levelwhen the comparing indicates a relatively decreasing impedance of thetarget tissue.
 14. The system of claim 13, wherein controllingcomprises: measuring a third impedance of the target tissue; comparingthe third impedance to at least one previously measured impedance. 15.The system of claim 14, wherein controlling comprises maintaining theenergy delivery at a present level when the comparing indicates arelatively decreasing impedance of the target tissue.
 16. The system ofclaim 14, wherein controlling comprises increasing the energy deliveryto a fifth level when the comparing indicates a relatively steadyimpedance of the target tissue.
 17. The system of claim 16, whereincontrolling comprises determining a state of cycle completion when thecomparing indicates a relatively increasing impedance of the targettissue.
 18. The system of claim 17, wherein controlling comprisesterminating energy delivery to the target tissue when the state of cyclecompletion is complete and the third impedance exceeds a final impedancelevel.
 19. The system of claim 17, wherein controlling comprises:measuring a fourth impedance of the target tissue; comparing the fourthimpedance to one or more of a previously measured impedance andincreasing the energy delivery to a sixth level when the state of cyclecompletion is complete and the fourth impedance is relatively steady.20. The system of claim 17, wherein controlling comprises: determining arate at which the relatively increasing impedance is increasing;comparing the rate to a first increase rate.
 21. The system of claim 20,wherein controlling comprises, when the rate is less than the firstincrease rate: measuring a fifth impedance of the target tissue;comparing the fifth impedance to one or more of a previously measuredimpedance and increasing the energy delivery to a seventh level when thestate of cycle completion is complete and the fifth impedance isrelatively steady.
 22. The system of claim 20, wherein controllingcomprises comparing the rate to a second increase rate when the rate isgreater than the first increase rate.
 23. The system of claim 22,wherein controlling comprises reducing the energy delivery to an eighthlevel when the rate is greater than the second increase rate.
 24. Thesystem of claim 23, wherein controlling comprises increasing the energydelivery at a second rate to a ninth level.
 25. The system of claim 22,wherein controlling comprises reducing the energy delivery to a tenthlevel when the rate is less than the second increase rate.
 26. A systemcomprising: an energy source; and an electrode array comprising bipolarelectrodes positioned so a first spacing between a first pair ofelectrodes is different relative to a second spacing between a secondpair of electrodes, wherein the electrode array and the energy sourceare coupled and configured to generate uniform energy density in targettissue in response to impedance of the target tissue.
 27. The system ofclaim 26, wherein the first spacing includes a first spacing amongcentral electrodes of the electrode array that is relatively larger thanthe second spacing between at least one pair of peripheral electrodes ofthe electrode array.
 28. The system of claim 26, wherein generatinguniform energy density in target tissue in response to impedanceincludes controlling the energy delivery in accordance with impedance,wherein controlling comprises: setting an initial impedance levelaccording to a type of the target tissue; measuring an impedance of thetarget tissue; initiating the energy delivery to the target tissue,wherein initiating the energy delivery includes energy delivery at afirst level that is determined according to the initial impedance level.29. The system of claim 28, wherein controlling further comprisesincreasing the energy delivery to a second level when the impedance isrelatively steady, and reducing the energy delivery to a third level andthen increasing the energy delivery at a first rate to a fourth levelwhen the impedance is relatively increasing.
 30. The system of claim 29,wherein controlling comprises maintaining the energy delivery at apresent level when the impedance is relatively decreasing.
 31. Thesystem of claim 30, wherein controlling comprises further increasing theenergy delivery to a fifth level when the impedance is relativelysteady.
 32. The system of claim 31, wherein controlling comprisesdetermining a state of cycle completion when the impedance is relativelyincreasing.
 33. The system of claim 32, wherein controlling comprisesterminating energy delivery to the target tissue when the state of cyclecompletion is complete and the impedance exceeds a final impedancelevel, and further increasing the energy delivery to a sixth level whenthe state of cycle completion is complete and the impedance isrelatively steady.
 34. The system of claim 32, wherein controllingcomprises further increasing the energy delivery to a seventh level whenthe state of cycle completion is complete, a rate at which the impedanceis increasing is less than a first increase rate, and the impedanceremains relatively steady.
 35. The system of claim 32, whereincontrolling comprises reducing the energy delivery to an eighth levelwhen the rate at which the impedance is increasing is greater than asecond increase rate, and then further increasing the energy delivery ata second rate to a ninth level.
 36. A method for controlling hemostasisin target tissue, comprising: configuring an array of bipolar electrodesin the target tissue so a first spacing between a pair of adjacentelectrodes is different relative to a second spacing between at leastone other pair of adjacent electrodes; delivering energy to the targettissue via the array; and controlling the delivering according toimpedance of the target tissue to generate uniform energy density in thetarget tissue.
 37. The method of claim 36, wherein configuring includespositioning each electrode of the electrode array at a selected depth inthe target tissue.
 38. The method of claim 36, further comprisinggenerating at least one plane of coagulated tissue in the target tissue.39. The method of claim 36, wherein the first spacing includes a firstspacing among central electrodes of the electrode array that isrelatively larger than a second spacing between at least one pair ofperipheral electrodes of the electrode array.
 40. The method of claim36, wherein the delivering includes generating a wave form that iscritically damped, wherein at least one damping parameter of the waveform is determined using at least one property of the target tissue. 41.The method of claim 36, wherein the delivering includes generating amodulated wave form, wherein at least one modulation parameter of themodulated wave form is determined using at least one property of thetarget tissue.
 42. The method of claim 36, wherein controlling thedelivering according to impedance includes controlling the delivering inaccordance with impedance, wherein controlling comprises: setting aninitial impedance level according to a type of the target tissue;measuring a first impedance of the target tissue; initiating the energydelivery to the target tissue when the first impedance is greater thanthe initial impedance level, wherein initiating the energy deliveryincludes energy delivery at a first level that is determined accordingto the initial impedance level.
 43. The method of claim 42, whereincontrolling comprises: measuring a second impedance of the targettissue; comparing the second impedance to the first impedance.
 44. Themethod of claim 43, wherein controlling comprises increasing energydelivery to a second level when the comparing indicates a relativelysteady impedance of the target tissue.
 45. The method of claim 43,wherein controlling comprises reducing energy delivery to a third levelwhen the comparing indicates a relatively increasing impedance of thetarget tissue.
 46. The method of claim 45, wherein controlling comprisesincreasing energy delivery at a first rate to a fourth level.
 47. Themethod of claim 45, wherein controlling comprises maintaining energydelivery at a present level when the comparing indicates a relativelydecreasing impedance of the target tissue.
 48. The method of claim 47,wherein controlling comprises: measuring a third impedance of the targettissue; comparing the third impedance to at least one previouslymeasured impedance.
 49. The method of claim 48, wherein controllingcomprises maintaining energy delivery at a present level when thecomparing indicates a relatively decreasing impedance of the targettissue.
 50. The method of claim 48, wherein controlling comprisesincreasing energy delivery to a fifth level when the comparing indicatesa relatively steady impedance of the target tissue.
 51. The method ofclaim 50, wherein controlling comprises determining a state of cyclecompletion when the comparing indicates a relatively increasingimpedance of the target tissue.
 52. The method of claim 51, whereincontrolling comprises terminating energy delivery to the target tissuewhen the state of cycle completion is complete and the third impedanceexceeds a final impedance level.
 53. The method of claim 51, whereincontrolling comprises: measuring a fourth impedance of the targettissue; comparing the fourth impedance to one or more of a previouslymeasured impedance and increasing energy delivery to a sixth level whenthe state of cycle completion is complete and the fourth impedance isrelatively steady.
 54. The method of claim 51, wherein controllingcomprises: determining a rate at which the relatively increasingimpedance is increasing; comparing the rate to a first increase rate.55. The method of claim 54, wherein controlling comprises, when the rateis less than the first increase rate: measuring a fifth impedance of thetarget tissue; comparing the fifth impedance to one or more of apreviously measured impedance and increasing energy delivery to aseventh level when the state of cycle completion is complete and thefifth impedance is relatively steady.
 56. The method of claim 54,wherein controlling comprises comparing the rate to a second increaserate when the rate is greater than the first increase rate.
 57. Themethod of claim 56, wherein controlling comprises reducing energydelivery to an eighth level when the rate is greater than the secondincrease rate.
 58. The method of claim 57, wherein controlling comprisesincreasing energy delivery at a second rate to a ninth level.
 59. Themethod of claim 56, wherein controlling comprises reducing energydelivery to a tenth level when the rate is less than the second increaserate.